Version:           4.1.96 (using Devel)
OS:                Linux
Installed from:    Compiled sources

I had a crash with 4.2.RC1 when switching from mail to calendar.

This is the BT:
Anwendung: Kontact (kontact), Signal SIGABRT

Thread 1 (Thread 0xb49fc6c0 (LWP 19426)):
[KCrash Handler]
#6  0xb7f3d430 in __kernel_vsyscall ()
#7  0xb58a6880 in raise () from /lib/tls/i686/cmov/libc.so.6
#8  0xb58a8248 in abort () from /lib/tls/i686/cmov/libc.so.6
#9  0xb5b4c795 in qt_message_output () from /usr/lib/libQtCore.so.4
#10 0xb5b4c872 in qFatal () from /usr/lib/libQtCore.so.4
#11 0xb5b4c915 in qt_assert () from /usr/lib/libQtCore.so.4
#12 0xb139af3d in KMail::MessageListView::Core::View::selectionAsMessageItemList (this=0x8c70c80, includeCollapsedChildren=true) at /build/buildd/kdepim-4.1.96/kmail/messagelistview/core/view.cpp:809
#13 0xb1341d14 in KMail::MessageListView::Widget::selectionAsMessageItemList (this=0x8c5ef58, includeCollapsedChildren=<value optimized out>)
    at /build/buildd/kdepim-4.1.96/kmail/messagelistview/widget.cpp:334
#14 0xb134401d in KMail::MessageListView::Widget::getSelectionStats (this=0x8c5ef58, selectedSernums=@0xbfa3d3f8, selectedVisibleSernums=@0xbfa3d3f4, allSelectedBelongToSameThread=0xbfa3d3ff, 
    includeCollapsedChildren=<value optimized out>) at /build/buildd/kdepim-4.1.96/kmail/messagelistview/widget.cpp:568
#15 0xb133a586 in KMail::MessageListView::Pane::getSelectionStats (this=0x8c633a0, selectedSernums=@0xbfa3d3f8, selectedVisibleSernums=@0xbfa3d3f4, allSelectedBelongToSameThread=0xbfa3d3ff, 
    includeCollapsedChildren=<value optimized out>) at /build/buildd/kdepim-4.1.96/kmail/messagelistview/pane.cpp:582
#16 0xb11df447 in KMMainWidget::updateMessageActions (this=0x8c5c410) at /build/buildd/kdepim-4.1.96/kmail/kmmainwidget.cpp:4326
#17 0xb11e09eb in KMMainWidget::initializeFilterActions (this=0x8c5c410) at /build/buildd/kdepim-4.1.96/kmail/kmmainwidget.cpp:4848
#18 0xb161e7c6 in KMailPart::guiActivateEvent (this=0x831f7b0, e=0xbfa3d958) at /build/buildd/kdepim-4.1.96/kmail/kmail_part.cpp:181
#19 0xb707de04 in KParts::Part::customEvent (this=0x831f7b0, ev=0xbfa3d958) at /build/buildd/kde4libs-4.1.96/kparts/part.cpp:321
#20 0xb5c547d7 in QObject::event () from /usr/lib/libQtCore.so.4
#21 0xb610c8ec in QApplicationPrivate::notify_helper () from /usr/lib/libQtGui.so.4
#22 0xb611472e in QApplication::notify () from /usr/lib/libQtGui.so.4
#23 0xb6c2d04d in KApplication::notify (this=0xbfa3f078, receiver=0x831f7b0, event=0xbfa3d958) at /build/buildd/kde4libs-4.1.96/kdeui/kernel/kapplication.cpp:307
#24 0xb5c44e61 in QCoreApplication::notifyInternal () from /usr/lib/libQtCore.so.4
#25 0xb708a20a in KParts::MainWindow::createGUI (this=0x8095808, part=0x8e2be70) at /usr/include/qt4/QtCore/qcoreapplication.h:209
#26 0xb77cae2e in Kontact::MainWindow::selectPlugin (this=0x8095808, plugin=0x8391040) at /build/buildd/kdepim-4.1.96/kontact/src/mainwindow.cpp:822
#27 0xb77cf464 in Kontact::MainWindow::qt_metacall (this=0x8095808, _c=QMetaObject::InvokeMetaMethod, _id=0, _a=0xbfa3dc9c)
    at /build/buildd/kdepim-4.1.96/obj-i486-linux-gnu/kontact/src/mainwindow.moc:106
#28 0xb5c59a60 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#29 0xb5c5a7e2 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#30 0xb77d1153 in Kontact::SidePaneBase::pluginSelected (this=0x817d3b0, _t1=0x8391040) at /build/buildd/kdepim-4.1.96/obj-i486-linux-gnu/kontact/src/sidepanebase.moc:82
#31 0xb77d11ef in Kontact::SidePaneBase::qt_metacall (this=0x817d3b0, _c=QMetaObject::InvokeMetaMethod, _id=0, _a=0xbfa3ddcc)
    at /build/buildd/kdepim-4.1.96/obj-i486-linux-gnu/kontact/src/sidepanebase.moc:70
#32 0xb77d149a in Kontact::IconSidePane::qt_metacall (this=0x817d3b0, _c=QMetaObject::InvokeMetaMethod, _id=27, _a=0xbfa3ddcc)
    at /build/buildd/kdepim-4.1.96/obj-i486-linux-gnu/kontact/src/iconsidepane.moc:130
#33 0xb5c59a60 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#34 0xb5c5a7e2 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#35 0xb77d1583 in Kontact::Navigator::pluginActivated (this=0x811b000, _t1=0x8391040) at /build/buildd/kdepim-4.1.96/obj-i486-linux-gnu/kontact/src/iconsidepane.moc:88
#36 0xb77d1f2d in Kontact::Navigator::qt_metacall (this=0x811b000, _c=QMetaObject::InvokeMetaMethod, _id=1, _a=0xbfa3dec8)
    at /build/buildd/kdepim-4.1.96/obj-i486-linux-gnu/kontact/src/iconsidepane.moc:75
#37 0xb5c59a60 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#38 0xb5c5a7e2 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#39 0xb6624f89 in QItemSelectionModel::currentChanged () from /usr/lib/libQtGui.so.4
#40 0xb662512d in QItemSelectionModel::setCurrentIndex () from /usr/lib/libQtGui.so.4
#41 0xb65d6fca in QAbstractItemView::mousePressEvent () from /usr/lib/libQtGui.so.4
#42 0xb6164949 in QWidget::event () from /usr/lib/libQtGui.so.4
#43 0xb649bfd3 in QFrame::event () from /usr/lib/libQtGui.so.4
#44 0xb65327df in QAbstractScrollArea::viewportEvent () from /usr/lib/libQtGui.so.4
#45 0xb65ddccf in QAbstractItemView::viewportEvent () from /usr/lib/libQtGui.so.4
#46 0xb6534d85 in ?? () from /usr/lib/libQtGui.so.4
#47 0xb5c4404a in QCoreApplicationPrivate::sendThroughObjectEventFilters () from /usr/lib/libQtCore.so.4
#48 0xb610c8ca in QApplicationPrivate::notify_helper () from /usr/lib/libQtGui.so.4
#49 0xb61150e1 in QApplication::notify () from /usr/lib/libQtGui.so.4
#50 0xb6c2d04d in KApplication::notify (this=0xbfa3f078, receiver=0x8171d98, event=0xbfa3e7a8) at /build/buildd/kde4libs-4.1.96/kdeui/kernel/kapplication.cpp:307
#51 0xb5c44e61 in QCoreApplication::notifyInternal () from /usr/lib/libQtCore.so.4
#52 0xb611436e in QApplicationPrivate::sendMouseEvent () from /usr/lib/libQtGui.so.4
#53 0xb617e656 in ?? () from /usr/lib/libQtGui.so.4
#54 0xb617d9e5 in QApplication::x11ProcessEvent () from /usr/lib/libQtGui.so.4
#55 0xb61a77aa in ?? () from /usr/lib/libQtGui.so.4
#56 0xb4f136f8 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#57 0xb4f16da3 in ?? () from /usr/lib/libglib-2.0.so.0
#58 0xb4f16f61 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#59 0xb5c6f478 in QEventDispatcherGlib::processEvents () from /usr/lib/libQtCore.so.4
#60 0xb61a6ea5 in ?? () from /usr/lib/libQtGui.so.4
#61 0xb5c4352a in QEventLoop::processEvents () from /usr/lib/libQtCore.so.4
#62 0xb5c436ea in QEventLoop::exec () from /usr/lib/libQtCore.so.4
#63 0xb5c45da5 in QCoreApplication::exec () from /usr/lib/libQtCore.so.4
#64 0xb610c767 in QApplication::exec () from /usr/lib/libQtGui.so.4
#65 0x0804c072 in main (argc=1, argv=0xbfa3f374) at /build/buildd/kdepim-4.1.96/kontact/src/main.cpp:218