Thanks for the bug report. Is this crash reproducible for you? I would assume that it depends on the contents of the closed tab (because I get no crashes if I close tabs). It would be helpful if you could provide step-by-step instructions how to get the crash.

Anwendung: Konqueror (konqueror), Signal SIGSEGV
[Thread debugging using libthread_db enabled]
[New Thread 0x7fc353e8f750 (LWP 14825)]
[KCrash handler]
#5  0x00007fc34f849771 in QWidget::isAncestorOf (this=0x2c2ed10, 
    child=0x371d240) at ../../include/QtGui/../../src/gui/kernel/qwidget.h:984
#6  0x00007fc34f840e43 in QStackedLayout::setCurrentIndex (this=0x27db710, 
    index=2) at kernel/qstackedlayout.cpp:321
#7  0x00007fc34fb83c42 in QStackedWidget::setCurrentIndex (
    this=<value optimized out>, index=57791040)
    at widgets/qstackedwidget.cpp:216
#8  0x00007fc34fb8cc3b in QTabWidgetPrivate::_q_showTab (this=0x2801220, 
    index=2) at widgets/qtabwidget.cpp:693
#9  0x00007fc34fb8cdd7 in QTabWidget::qt_metacall (this=0x27dae40, 
    _c=QMetaObject::InvokeMetaMethod, _id=<value optimized out>, 
    _a=0x7fff5bec7d50) at .moc/release-shared/moc_qtabwidget.cpp:115
#10 0x00007fc352bbfc35 in KTabWidget::qt_metacall (this=0x2c2ed10, 
    _c=57791040, _id=0, _a=0x1a)
    at /var/tmp/portage/kde-base/kdelibs-4.1.1-r4/work/kdelibs_build/kdeui/ktabwidget.moc:121
#11 0x00007fc353a26645 in KonqFrameTabs::qt_metacall (this=0x2c2ed10, 
    _c=57791040, _id=0, _a=0x1a)
    at /var/tmp/portage/kde-base/konqueror-4.1.1/work/konqueror_build/apps/konqueror/src/konqtabs.moc:93
#12 0x00007fc350921d53 in QMetaObject::activate (sender=0x27e0190, 
    from_signal_index=<value optimized out>, to_signal_index=27, argv=0x1a)
    at kernel/qobject.cpp:3028
#13 0x00007fc350922ffd in QMetaObject::activate (sender=0x27e0190, 
    m=<value optimized out>, local_signal_index=0, argv=0x7fff5bec7d50)
    at kernel/qobject.cpp:3098
#14 0x00007fc34fb8624b in QTabBar::currentChanged (this=0x2c2ed10, _t1=2)
    at .moc/release-shared/moc_qtabbar.cpp:155
#15 0x00007fc34fb87285 in QTabBar::setCurrentIndex (this=0x27e0190, index=2)
    at widgets/qtabbar.cpp:965
#16 0x00007fc34fb8b7ec in QTabWidget::setCurrentIndex (
    this=<value optimized out>, index=57791040) at widgets/qtabwidget.cpp:624
#17 0x00007fc353a13f1a in KonqViewManager::showTab (this=0x236cc10, 
    view=0x3fff480)
    at /var/tmp/portage/kde-base/konqueror-4.1.1/work/konqueror-4.1.1/apps/konqueror/src/konqviewmanager.cpp:483
#18 0x00007fc353a5719c in KonqMainWindow::slotAddTab (this=0x2314d00)
    at /var/tmp/portage/kde-base/konqueror-4.1.1/work/konqueror-4.1.1/apps/konqueror/src/konqmainwindow.cpp:2335
#19 0x00007fc353a60f5d in KonqMainWindow::qt_metacall (this=0x2314d00, 
    _c=QMetaObject::InvokeMetaMethod, _id=<value optimized out>, 
    _a=0x7fff5bec80c0)
    at /var/tmp/portage/kde-base/konqueror-4.1.1/work/konqueror_build/apps/konqueror/src/konqmainwindow.moc:388
#20 0x00007fc350921d53 in QMetaObject::activate (sender=0x2638b10, 
    from_signal_index=<value optimized out>, to_signal_index=6, argv=0x1a)
    at kernel/qobject.cpp:3028
#21 0x00007fc35092200a in QMetaObject::activate (sender=0x2638b10, 
    m=<value optimized out>, from_local_signal_index=128, 
    to_local_signal_index=2, argv=0x7fff5bec80c0) at kernel/qobject.cpp:3118
#22 0x00007fc34f8067ff in QAction::triggered (this=0x2c2ed10, _t1=false)
    at .moc/release-shared/moc_qaction.cpp:216
#23 0x00007fc34f806e40 in QAction::activate (this=0x2638b10, 
    event=<value optimized out>) at kernel/qaction.cpp:1131
#24 0x00007fc34f80a11e in QAction::event (this=0x2c2ed10, 
    e=<value optimized out>) at kernel/qaction.cpp:1050
#25 0x00007fc34f85c8e7 in QWidgetAction::event (this=0x2638b10, 
    event=0x7fff5bec84f0) at kernel/qwidgetaction.cpp:236
#26 0x00007fc34f80c0b3 in QApplicationPrivate::notify_helper (
    this=<value optimized out>, receiver=0x2638b10, e=0x7fff5bec84f0)
    at kernel/qapplication.cpp:3809
#27 0x00007fc34f81351c in QApplication::notify (this=0x7fff5bec9960, 
    receiver=0x2638b10, e=0x7fff5bec84f0) at kernel/qapplication.cpp:3399
#28 0x00007fc352aef7eb in KApplication::notify (this=0x7fff5bec9960, 
    receiver=0x2638b10, event=0x7fff5bec84f0)
    at /var/tmp/portage/kde-base/kdelibs-4.1.1-r4/work/kdelibs-4.1.1/kdeui/kernel/kapplication.cpp:311
#29 0x00007fc35090f207 in QCoreApplication::notifyInternal (
    this=0x7fff5bec9960, receiver=0x2638b10, event=0x7fff5bec84f0)
    at kernel/qcoreapplication.cpp:593
#30 0x00007fc34f83cfad in QShortcutMap::dispatchEvent (
    this=<value optimized out>, e=0x7fff5bec8900)
    at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:215
#31 0x00007fc34f83e4f5 in QShortcutMap::tryShortcutEvent (this=0x22bf6f0, 
    w=<value optimized out>, e=0x7fff5bec8900) at kernel/qshortcutmap.cpp:368
#32 0x00007fc34f81367d in QApplication::notify (this=<value optimized out>, 
    receiver=0x2314d00, e=0x7fff5bec8900) at kernel/qapplication.cpp:3436
#33 0x00007fc352aef7eb in KApplication::notify (this=0x7fff5bec9960, 
    receiver=0x2314d00, event=0x7fff5bec8900)
    at /var/tmp/portage/kde-base/kdelibs-4.1.1-r4/work/kdelibs-4.1.1/kdeui/kernel/kapplication.cpp:311
#34 0x00007fc35090f207 in QCoreApplication::notifyInternal (
    this=0x7fff5bec9960, receiver=0x2314d00, event=0x7fff5bec8900)
    at kernel/qcoreapplication.cpp:593
#35 0x00007fc34f860533 in qt_sendSpontaneousEvent (receiver=0x1a, 
    event=<value optimized out>)
    at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:218
#36 0x00007fc34f88a9f5 in QKeyMapper::sendKeyEvent (keyWidget=0x2314d00, 
    grab=<value optimized out>, type=QEvent::KeyPress, code=84, modifiers=
      {i = 1542229552}, text=@0x7fff5bec8de0, autorepeat=false, count=1, 
    nativeScanCode=28, nativeVirtualKey=116, nativeModifiers=4)
    at kernel/qkeymapper_x11.cpp:1658
#37 0x00007fc34f88cc28 in QKeyMapperPrivate::translateKeyEvent (
    this=0x7fff5bec8ab0, keyWidget=0x2314d00, event=0x7fff5bec92d0, grab=64)
    at kernel/qkeymapper_x11.cpp:1629
#38 0x00007fc34f86aa4f in QApplication::x11ProcessEvent (this=0x7fff5bec9960, 
    event=0x7fff5bec92d0) at kernel/qapplication_x11.cpp:3059
#39 0x00007fc34f88db4c in x11EventSourceDispatch (s=<value optimized out>, 
    callback=0, user_data=0x0) at kernel/qguieventdispatcher_glib.cpp:148
#40 0x00007fc34c009f42 in IA__g_main_context_dispatch (context=0x22c1d20)
    at gmain.c:2142
#41 0x00007fc34c00d65d in g_main_context_iterate (context=0x22c1d20, block=1, 
    dispatch=1, self=<value optimized out>) at gmain.c:2776
#42 0x00007fc34c00d81b in IA__g_main_context_iteration (context=0x22c1d20, 
    may_block=1) at gmain.c:2839
#43 0x00007fc350934d6e in QEventDispatcherGlib::processEvents (
    this=0x22baac0, flags=<value optimized out>)
    at kernel/qeventdispatcher_glib.cpp:325
#44 0x00007fc34f88d75f in QGuiEventDispatcherGlib::processEvents (
    this=0x2c2ed10, flags=<value optimized out>)
    at kernel/qguieventdispatcher_glib.cpp:204
#45 0x00007fc35090dc7d in QEventLoop::processEvents (
    this=<value optimized out>, flags={i = 1542231712})
    at kernel/qeventloop.cpp:149
#46 0x00007fc35090ddf1 in QEventLoop::exec (this=0x7fff5bec96e0, flags=
      {i = 1542231792}) at kernel/qeventloop.cpp:200
#47 0x00007fc35090ffbc in QCoreApplication::exec ()
    at kernel/qcoreapplication.cpp:851
#48 0x00007fc34f80bf4a in QApplication::exec ()
    at kernel/qapplication.cpp:3337
#49 0x00007fc353a834f2 in kdemain (argc=<value optimized out>, 
    argv=<value optimized out>)
    at /var/tmp/portage/kde-base/konqueror-4.1.1/work/konqueror-4.1.1/apps/konqueror/src/konqmain.cpp:227
#50 0x00007fc34cfcb486 in __libc_start_main (main=0x400a40 <main>, argc=2, 
    ubp_av=0x7fff5beca168, init=0x400a70 <__libc_csu_init>, 
    fini=<value optimized out>, rtld_fini=<value optimized out>, 
    stack_end=0x7fff5beca158) at libc-start.c:226
#51 0x0000000000400979 in _start ()
#0  0x00007fc34d04cca1 in nanosleep () from /lib64/libc.so.6


I am definitely not sure if I "hit the right bug"...

Wasn't able to do it twice...

I can confirm the crash with trunk compiled yesterday evening (upcoming 4.2). The backtrace from comment #2 is unrelated.

The attached backtrace shows, that the reason is, that within the KonqMainWindow::slotPartActivated(KParts::Part *part) method the call m_mapViews.value( static_cast<KParts::ReadOnlyPart *>(part) ); returns NULL. I added a Q_ASSERT(newView) to let it at least assert as soon as possible. Not sure there what would be the right fix.

backtrace;
[KCrash Handler]
#5  0x00007f6727ce5054 in KonqView::isPassiveMode (this=0x0) at /home/kde4/svn/_src/KDE/kdebase/apps/konqueror/src/konqview.h:286
#6  0x00007f6727d35047 in KonqMainWindow::slotPartActivated (this=0x870ac0, part=0x10765a0) at /home/kde4/svn/_src/KDE/kdebase/apps/konqueror/src/konqmainwindow.cpp:1979
#7  0x00007f6727cf5842 in KonqViewManager::emitActivePartChanged (this=0x875450) at /home/kde4/svn/_src/KDE/kdebase/apps/konqueror/src/konqviewmanager.cpp:1023
#8  0x00007f6727cf5c2a in KonqViewManager::doSetActivePart (this=0x875450, part=0x10765a0) at /home/kde4/svn/_src/KDE/kdebase/apps/konqueror/src/konqviewmanager.cpp:994
#9  0x00007f6727cf5c55 in KonqViewManager::setActivePart (this=0x875450, part=0x10765a0) at /home/kde4/svn/_src/KDE/kdebase/apps/konqueror/src/konqviewmanager.cpp:955
#10 0x00007f67249356cc in KParts::PartManager::eventFilter (this=0x875450, obj=0x109e920, ev=0x7fff301cc530) at /home/kde4/svn/_src/KDE/kdelibs/kparts/partmanager.cpp:282
#11 0x00007f67262cc743 in QCoreApplicationPrivate::sendThroughApplicationEventFilters (this=0x623310, receiver=0x109e920, event=0x7fff301cc530) at kernel/qcoreapplication.cpp:682
#12 0x00007f6724d3bc26 in QApplicationPrivate::notify_helper (this=0x623310, receiver=0x109e920, e=0x7fff301cc530) at kernel/qapplication.cpp:3784
#13 0x00007f6724d3d9bf in QApplication::notify (this=0x7fff301ce960, receiver=0x109e920, e=0x7fff301cc530) at kernel/qapplication.cpp:3774
#14 0x00007f6726f0ba7e in KApplication::notify (this=0x7fff301ce960, receiver=0x109e920, event=0x7fff301cc530) at /home/kde4/svn/_src/KDE/kdelibs/kdeui/kernel/kapplication.cpp:307
#15 0x00007f67262ce132 in QCoreApplication::notifyInternal (this=0x7fff301ce960, receiver=0x109e920, event=0x7fff301cc530) at kernel/qcoreapplication.cpp:589
#16 0x00007f67262d1b71 in QCoreApplication::sendEvent (receiver=0x109e920, event=0x7fff301cc530) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:215
#17 0x00007f6724d3ef2c in QApplicationPrivate::setFocusWidget (focus=0x109e920, reason=Qt::OtherFocusReason) at kernel/qapplication.cpp:2005
#18 0x00007f6724d8e436 in QWidget::setFocus (this=0x109e920, reason=Qt::OtherFocusReason) at kernel/qwidget.cpp:5382
#19 0x00007f6718b04d72 in QWidget::setFocus (this=0x109e920) at /home/kde4/qt4-copy/include/QtGui/qwidget.h:409
#20 0x00007f6718b79b4a in DOM::DocumentImpl::setFocusNode (this=0x1665000, newFocusNode=0x2c48f00) at /home/kde4/svn/_src/KDE/kdelibs/khtml/xml/dom_docimpl.cpp:2445
#21 0x00007f6718b20be3 in KHTMLPart::checkCompleted (this=0x10765a0) at /home/kde4/svn/_src/KDE/kdelibs/khtml/khtml_part.cpp:2225
#22 0x00007f6718b243e9 in KHTMLPart::slotFinishedParsing (this=0x10765a0) at /home/kde4/svn/_src/KDE/kdelibs/khtml/khtml_part.cpp:2104
#23 0x00007f6718b32c25 in KHTMLPart::closeUrl (this=0x10765a0) at /home/kde4/svn/_src/KDE/kdelibs/khtml/khtml_part.cpp:869
#24 0x00007f6718b36f25 in ~KHTMLPart (this=0x10765a0) at /home/kde4/svn/_src/KDE/kdelibs/khtml/khtml_part.cpp:525
#25 0x00007f6727cefece in ~KonqView (this=0x10769a0) at /home/kde4/svn/_src/KDE/kdebase/apps/konqueror/src/konqview.cpp:132
#26 0x00007f6727cf9f79 in KonqViewManager::removeTab (this=0x875450, currentFrame=0x1064448, emitAboutToRemoveSignal=true)
    at /home/kde4/svn/_src/KDE/kdebase/apps/konqueror/src/konqviewmanager.cpp:389
#27 0x00007f6727d33420 in KonqMainWindow::slotRemoveTab (this=0x870ac0) at /home/kde4/svn/_src/KDE/kdebase/apps/konqueror/src/konqmainwindow.cpp:2490

This might be related (one crash when I closed a tab):

Application: Konqueror (konqueror), signal SIGABRT
[?1034h[Thread debugging using libthread_db enabled]
[Current thread is 1 (Thread 0xb5e5a700 (LWP 7021))]

Thread 1 (Thread 0xb5e5a700 (LWP 7021)):
[KCrash Handler]
#6  0xffffe430 in __kernel_vsyscall ()
#7  0xb640d990 in raise () from /lib/libc.so.6
#8  0xb640f2c8 in abort () from /lib/libc.so.6
#9  0xb71518d5 in qt_message_output(QtMsgType, char const*) () from /usr/lib/libQtCore.so.4
#10 0xb71519b2 in qFatal(char const*, ...) () from /usr/lib/libQtCore.so.4
#11 0xb717d7d4 in QListData::detach2() () from /usr/lib/libQtCore.so.4
#12 0xb7260f37 in ?? () from /usr/lib/libQtCore.so.4
#13 0xb7260626 in QObject::~QObject() () from /usr/lib/libQtCore.so.4
#14 0xb697bc1f in QWidget::~QWidget() () from /usr/lib/libQtGui.so.4
#15 0xb6cf2e30 in QMenu::~QMenu() () from /usr/lib/libQtGui.so.4
#16 0xb78c9adf in ~KMenu (this=0xa58fbf0) at /usr/src/debug/kdelibs-4.2.0/kdeui/widgets/kmenu.cpp:173
#17 0xb771bfd6 in ~KSelectAction (this=0x8a90528) at /usr/src/debug/kdelibs-4.2.0/kdeui/actions/kselectaction.cpp:100
#18 0xb7257c1f in QObjectPrivate::deleteChildren() () from /usr/lib/libQtCore.so.4
#19 0xb7260763 in QObject::~QObject() () from /usr/lib/libQtCore.so.4
#20 0xb691e66a in QAction::~QAction() () from /usr/lib/libQtGui.so.4
#21 0xb6980028 in QWidgetAction::~QWidgetAction() () from /usr/lib/libQtGui.so.4
#22 0xb7710318 in ~KAction (this=0x94fa720) at /usr/src/debug/kdelibs-4.2.0/kdeui/actions/kaction.cpp:128
#23 0xb771c0a2 in ~KSelectAction (this=0x94fa720) at /usr/src/debug/kdelibs-4.2.0/kdeui/actions/kselectaction.cpp:101
#24 0xb7712318 in ~KCodecAction (this=0x94fa720) at /usr/src/debug/kdelibs-4.2.0/kdeui/actions/kcodecaction.cpp:86
#25 0xb7257c1f in QObjectPrivate::deleteChildren() () from /usr/lib/libQtCore.so.4
#26 0xb7260763 in QObject::~QObject() () from /usr/lib/libQtCore.so.4
#27 0xb7da9305 in ~Part (this=0xad95cd8, __vtt_parm=0xb3f03a08) at /usr/src/debug/kdelibs-4.2.0/kparts/part.cpp:213
#28 0xb7daa98a in ~ReadOnlyPart (this=0xad95cd8, __vtt_parm=0xb3f03a04) at /usr/src/debug/kdelibs-4.2.0/kparts/part.cpp:460
#29 0xb3a295e1 in ~KHTMLPart (this=0xad95cd8) at /usr/src/debug/kdelibs-4.2.0/khtml/khtml_part.cpp:603
#30 0xb7e91d08 in ~KonqView (this=0x9e30cf8) at /usr/src/debug/kdebase-4.2.0/apps/konqueror/src/konqview.cpp:132
#31 0xb7e96fdc in KonqViewManager::removeTab (this=0x80a6650, currentFrame=0x94b5fac, emitAboutToRemoveSignal=true) at /usr/src/debug/kdebase-4.2.0/apps/konqueror/src/konqviewmanager.cpp:389
#32 0xb7ec6bd5 in KonqMainWindow::slotRemoveTabPopupDelayed (this=0x80b0d40) at /usr/src/debug/kdebase-4.2.0/apps/konqueror/src/konqmainwindow.cpp:2533
#33 0xb7eeaabc in KonqMainWindow::qt_metacall (this=0x80b0d40, _c=QMetaObject::InvokeMetaMethod, _id=82, _a=0xbfc97538) at /usr/src/debug/kdebase-4.2.0/build/apps/konqueror/src/konqmainwindow.moc:414
#34 0xb725e580 in QMetaObject::activate(QObject*, int, int, void**) () from /usr/lib/libQtCore.so.4
#35 0xb725f302 in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) () from /usr/lib/libQtCore.so.4
#36 0xb7264947 in ?? () from /usr/lib/libQtCore.so.4
#37 0xb7264a6c in ?? () from /usr/lib/libQtCore.so.4
#38 0xb725904f in QObject::event(QEvent*) () from /usr/lib/libQtCore.so.4
#39 0xb69228fc in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/libQtGui.so.4
#40 0xb692a75e in QApplication::notify(QObject*, QEvent*) () from /usr/lib/libQtGui.so.4
#41 0xb77ea91d in KApplication::notify (this=0xbfc97e20, receiver=0x8d882a8, event=0xbfc979f0) at /usr/src/debug/kdelibs-4.2.0/kdeui/kernel/kapplication.cpp:307
#42 0xb7249961 in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib/libQtCore.so.4
#43 0xb7277b86 in ?? () from /usr/lib/libQtCore.so.4
#44 0xb7274060 in ?? () from /usr/lib/libQtCore.so.4
#45 0xb61e79a8 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#46 0xb61eb063 in ?? () from /usr/lib/libglib-2.0.so.0
#47 0xb61eb221 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#48 0xb7273fb8 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#49 0xb69bb7c5 in ?? () from /usr/lib/libQtGui.so.4
#50 0xb724801a in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#51 0xb72481da in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQtCore.so.4
#52 0xb724a895 in QCoreApplication::exec() () from /usr/lib/libQtCore.so.4
#53 0xb6922777 in QApplication::exec() () from /usr/lib/libQtGui.so.4
#54 0xb7f116ff in kdemain (argc=2, argv=0xbfc98174) at /usr/src/debug/kdebase-4.2.0/apps/konqueror/src/konqmain.cpp:257
#55 0x08048772 in main (argc=) at /usr/src/debug/kdebase-4.2.0/build/apps/konqueror/src/konqueror_dummy.cpp:3

(In reply to comment #4)
> This might be related (one crash when I closed a tab):

Your backtrace looks different, the crash is probably unrelated. If you can reproduce the issue, please file a new bug report and describe in detail what you did before the crash. Thanks!

BTW, is the crash from the original report still reproducible in 4.2.0? If not, I suppose that Sebastian was right in http://bugs.kde.org/show_bug.cgi?id=173473#c8 and it's a duplicate of an issue that is now fixed.

I upgraded to KDE4.2.1 and QT4.5 on opensuse.

Since then (and not before), I have this crash. I suppose that in my case it is related to the upgrade of QT. 
With KDE4.2.6x the problem is the same

(In reply to comment #6)
> I upgraded to KDE4.2.1 and QT4.5 on opensuse.
> Since then (and not before), I have this crash.

Do you really have the same backtrace? If not, please file a new bug report and paste the backtrace there, see

http://techbase.kde.org/Development/Tutorials/Debugging/How_to_create_useful_crash_reports

In any case, please describe in detail what you did before the crash (e.g., what was open in the tab that you closed to get the crash). Thanks!

> With KDE4.2.6x the problem is the same

What is KDE 4.2.6x? A typo probably?

Please disregard my previous comment. I mistakenly thought that I was back to khtml after testing qtwebkit which seems to be the cause. I will dig into that direction.

> What is KDE 4.2.6x? A typo probably?
KDE 4.2.65 as numbered in buildservice

Marking as duplicate (see my comment 5). Please reopen or file a new bug if you see the crash from the original report again in KDE 4.2.1 or later. Thanks!

*** This bug has been marked as a duplicate of bug 173473 ***