After having compiled KDE myself, here a somewhat more verbose backtrace (KDE Version 4.00.80 >= 20080104 and gcc version 4.1.2 20070214 on a gentoo machine)

Using host libthread_db library "/lib/libthread_db.so.1".
[Thread debugging using libthread_db enabled]
[New Thread 0xb60708e0 (LWP 14542)]
[KCrash handler]
#6  0xffffe410 in __kernel_vsyscall ()
#7  0xb61de1f1 in *__GI_raise (sig=6)
    at ../nptl/sysdeps/unix/sysv/linux/raise.c:64
#8  0xb61df9b8 in *__GI_abort () at abort.c:88
#9  0xb7dd5265 in qt_message_output (msgType=QtFatalMsg, 
    buf=0xbfd3525c "ASSERT failure in QList<T>::at: \"index out of range\", file ../../include/QtCore/../../src/corelib/tools/qlist.h, line 386")
    at global/qglobal.cpp:2162
#10 0xb7dd532a in qFatal (
    msg=0xb7edc714 "ASSERT failure in %s: \"%s\", file %s, line %d")
    at global/qglobal.cpp:2393
#11 0xb7dd537c in qt_assert_x (where=0xb6acfec7 "QList<T>::at", 
    what=0xb6acfeb4 "index out of range", 
    file=0xb6acfc50 "../../include/QtCore/../../src/corelib/tools/qlist.h", 
    line=386) at global/qglobal.cpp:1927
#12 0xb6abca3f in QUndoStack::undoText (this=0x83b2500)
    at ../../include/QtCore/../../src/corelib/tools/qlist.h:386
#13 0xb6abd352 in QUndoStackPrivate::setIndex (this=0x83b8520, idx=17, 
    clean=false) at util/qundostack.cpp:410
#14 0xb6abd732 in QUndoStack::redo (this=0x83b2500) at util/qundostack.cpp:694
#15 0xb6acf450 in QUndoStack::qt_metacall (this=0x83b2500, 
    _c=QMetaObject::InvokeMetaMethod, _id=9, _a=0xbfd3786c)
    at .moc/debug-shared/moc_qundostack.cpp:98
#16 0xb7ab74a2 in KUndoStack::qt_metacall (this=0x83b2500, 
    _c=QMetaObject::InvokeMetaMethod, _id=13, _a=0xbfd3786c)
    at /var/tmp/portage/kde-base/kdelibs-9999.4/work/kdelibs_build/kdeui/kundostack.moc:56
#17 0xb7ebb124 in QMetaObject::activate (sender=0x83b4050, 
    from_signal_index=5, to_signal_index=6, argv=<value optimized out>)
    at kernel/qobject.cpp:3083
#18 0xb7ebb512 in QMetaObject::activate (sender=0x83b4050, m=0xb6c4e4c0, 
    from_local_signal_index=1, to_local_signal_index=2, argv=0xbfd3786c)
    at kernel/qobject.cpp:3162
#19 0xb64fec03 in QAction::triggered (this=0x83b4050, _t1=false)
    at .moc/debug-shared/moc_qaction.cpp:208
#20 0xb64ff6fd in QAction::activate (this=0x83b4050, event=QAction::Trigger)
    at kernel/qaction.cpp:1116
#21 0xb6928090 in QToolButton::nextCheckState (this=0x84038c0)
    at ../../include/QtGui/../../src/gui/kernel/qaction.h:190
#22 0xb684a27d in QAbstractButtonPrivate::click (this=0x83c1650)
    at widgets/qabstractbutton.cpp:515
#23 0xb684a50e in QAbstractButton::mouseReleaseEvent (this=0x84038c0, 
    e=0xbfd37fa4) at widgets/qabstractbutton.cpp:1102
#24 0xb692818c in QToolButton::mouseReleaseEvent (this=0x84038c0, 
    e=0xbfd37fa4) at widgets/qtoolbutton.cpp:658
#25 0xb6558bf5 in QWidget::event (this=0x84038c0, event=0xbfd37fa4)
    at kernel/qwidget.cpp:6129
#26 0xb6849013 in QAbstractButton::event (this=0x84038c0, e=0x38ce)
    at widgets/qabstractbutton.cpp:1064
#27 0xb69279c4 in QToolButton::event (this=0x84038c0, e=0xbfd37fa4)
    at widgets/qtoolbutton.cpp:1075
#28 0xb65060ca in QApplicationPrivate::notify_helper (this=0x831c9d8, 
    receiver=0x84038c0, e=0xbfd37fa4) at kernel/qapplication.cpp:3558
#29 0xb6507c6c in QApplication::notify (this=0xbfd3852c, receiver=0x84038c0, 
    e=0xbfd37fa4) at kernel/qapplication.cpp:3257
#30 0xb7a35783 in KApplication::notify (this=0xbfd3852c, receiver=0x84038c0, 
    event=0xbfd37fa4)
    at /var/tmp/portage/kde-base/kdelibs-9999.4/work/kdelibs-9999.4/kdeui/kernel/kapplication.cpp:314
#31 0xb7ea7cab in QCoreApplication::notifyInternal (this=0xbfd3852c, 
    receiver=0x84038c0, event=0xbfd37fa4) at kernel/qcoreapplication.cpp:532
#32 0xb656b908 in QETWidget::translateMouseEvent (this=0x84038c0, 
    event=0xbfd38368)
    at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:205
#33 0xb656a16e in QApplication::x11ProcessEvent (this=0xbfd3852c, 
    event=0xbfd38368) at kernel/qapplication_x11.cpp:2917
#34 0xb658fef5 in QEventDispatcherX11::processEvents (this=0x831c8e8, 
    flags=@0xbfd38454) at kernel/qeventdispatcher_x11.cpp:127
#35 0xb7ea70c1 in QEventLoop::processEvents (this=0xbfd384c0, 
    flags=@0xbfd38488) at kernel/qeventloop.cpp:142
#36 0xb7ea71ca in QEventLoop::exec (this=0xbfd384c0, flags=@0xbfd384c8)
    at kernel/qeventloop.cpp:188
#37 0xb7ea9556 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:761
#38 0xb65056c7 in QApplication::exec () at kernel/qapplication.cpp:3055
#39 0x08230972 in main (argc=3, argv=0xbfd38684)
    at /var/tmp/portage/kde-base/kdesdk-9999.4/work/kdesdk-9999.4/umbrello/umbrello/main.cpp:111
#40 0xb61cafdc in __libc_start_main (main=0x8230340 <main>, argc=3, 
    ubp_av=0xbfd38684, init=0x82af290 <__libc_csu_init>, 
    fini=0x82af280 <__libc_csu_fini>, rtld_fini=0xb7f6b100 <_dl_fini>, 
    stack_end=0xbfd3867c) at libc-start.c:229
#41 0x08079701 in _start ()
#0  0xffffe410 in __kernel_vsyscall ()

Still valid in a current KDE SVN build

Still valid in KDE 4.0.82 >= 20080610 (OpenSuse KDE4 Builds)

Application: Umbrello UML Modeller (umbrello), signal SIGSEGV
[?1034h[Thread debugging using libthread_db enabled]
[New Thread 0xb60b26d0 (LWP 2657)]
[KCrash handler]
#6  QUndoCommand::text (this=0x8b06968)
    at ../../include/QtCore/../../src/corelib/arch/qatomic_i386.h:121
#7  0xb6b543c5 in QUndoStack::undoText (this=0x890a578)
    at util/qundostack.cpp:795
#8  0xb6b553d0 in QUndoStackPrivate::setIndex (this=0x8935e80, idx=17, 
    clean=false) at util/qundostack.cpp:401
#9  0xb6b556dd in QUndoStack::redo (this=0x890a578) at util/qundostack.cpp:685
#10 0xb6b67083 in QUndoStack::qt_metacall (this=0x890a578, 
    _c=QMetaObject::InvokeMetaMethod, _id=9, _a=0xbfd6135c)
    at .moc/release-shared/moc_qundostack.cpp:99
#11 0xb78fd902 in KUndoStack::qt_metacall (this=0x890a578, 
    _c=QMetaObject::InvokeMetaMethod, _id=13, _a=0xbfd6135c)
    at /usr/src/debug/kdelibs-4.0.82/build/kdeui/kundostack.moc:57
#12 0xb72d73fa in QMetaObject::activate (sender=0x8937940, 
    from_signal_index=5, to_signal_index=6, argv=0xbfd6135c)
    at kernel/qobject.cpp:3007
#13 0xb72d76f0 in QMetaObject::activate (sender=0x8937940, m=0xb6c12e18, 
    from_local_signal_index=1, to_local_signal_index=2, argv=0xbfd6135c)
    at kernel/qobject.cpp:3100
#14 0xb65f3941 in QAction::triggered (this=0x8937940, _t1=false)
    at .moc/release-shared/moc_qaction.cpp:216
#15 0xb65f42af in QAction::activate (this=0x8937940, event=QAction::Trigger)
    at kernel/qaction.cpp:1119
#16 0xb69b9162 in QToolButton::nextCheckState (this=0x0)
    at ../../include/QtGui/../../src/gui/kernel/qaction.h:201
#17 0xb68ef5e3 in QAbstractButtonPrivate::click (this=0x896f7c0)
    at widgets/qabstractbutton.cpp:525
#18 0xb68ef886 in QAbstractButton::mouseReleaseEvent (this=0x89ab390, 
    e=0xbfd61928) at widgets/qabstractbutton.cpp:1112
#19 0xb69b95fc in QToolButton::mouseReleaseEvent (this=0x89ab390, e=0xbfd61928)
    at widgets/qtoolbutton.cpp:675
#20 0xb664b176 in QWidget::event (this=0x89ab390, event=0xbfd61928)
    at kernel/qwidget.cpp:6927
#21 0xb68ee70e in QAbstractButton::event (this=0x89ab390, e=0xbfd61928)
    at widgets/qabstractbutton.cpp:1074
#22 0xb69b9124 in QToolButton::event (this=0x89ab390, e=0xbfd61928)
    at widgets/qtoolbutton.cpp:1105
#23 0xb65f8ecc in QApplicationPrivate::notify_helper (this=0x886a698, 
    receiver=0x89ab390, e=0xbfd61928) at kernel/qapplication.cpp:3772
#24 0xb65ffca7 in QApplication::notify (this=0xbfd62060, receiver=0x89ab390, 
    e=0xbfd61928) at kernel/qapplication.cpp:3501
#25 0xb787709d in KApplication::notify (this=0xbfd62060, receiver=0x89ab390, 
    event=0xbfd61928)
    at /usr/src/debug/kdelibs-4.0.82/kdeui/kernel/kapplication.cpp:311
#26 0xb72c5b51 in QCoreApplication::notifyInternal (this=0xbfd62060, 
    receiver=0x89ab390, event=0xbfd61928) at kernel/qcoreapplication.cpp:583
#27 0xb6600fae in QApplicationPrivate::sendMouseEvent (receiver=0x89ab390, 
    event=0xbfd61928, alienWidget=0x89ab390, nativeWidget=0x88e1cd0, 
    buttonDown=0xb6c29c10, lastMouseReceiver=@0xb6c29c14)
    at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:218
#28 0xb665e1e8 in QETWidget::translateMouseEvent (this=0x88e1cd0, 
    event=0xbfd61edc) at kernel/qapplication_x11.cpp:4131
#29 0xb665d5a4 in QApplication::x11ProcessEvent (this=0xbfd62060, 
    event=0xbfd61edc) at kernel/qapplication_x11.cpp:3131
#30 0xb66833ae in QEventDispatcherX11::processEvents (this=0x886a180, flags=
      {i = -1076486280}) at kernel/qeventdispatcher_x11.cpp:134
#31 0xb72c42ca in QEventLoop::processEvents (this=0xbfd61fe0, flags=
      {i = -1076486216}) at kernel/qeventloop.cpp:149
#32 0xb72c448a in QEventLoop::exec (this=0xbfd61fe0, flags={i = -1076486168})
    at kernel/qeventloop.cpp:196
#33 0xb72c666d in QCoreApplication::exec () at kernel/qcoreapplication.cpp:845
#34 0xb65f8d47 in QApplication::exec () at kernel/qapplication.cpp:3304
#35 0x086a1f05 in main (argc=1, argv=0xbfd621d4)
    at /usr/src/debug/kdesdk-4.0.82/umbrello/umbrello/main.cpp:110
#0  0xffffe422 in __kernel_vsyscall ()

Still crashes in KDE-4.1.1

Backtrace:

Application: Umbrello UML Modeller (umbrello), signal SIGABRT
[Thread debugging using libthread_db enabled]
[New Thread 0xb5f67700 (LWP 3233)]
[KCrash handler]
#6  0xffffe424 in __kernel_vsyscall ()
#7  0xb6141690 in *__GI_raise (sig=6)
    at ../nptl/sysdeps/unix/sysv/linux/raise.c:64
#8  0xb6142ed8 in *__GI_abort () at abort.c:88
#9  0xb722d36f in qt_message_output (msgType=QtFatalMsg, 
    buf=0xbf8e1800 "ASSERT failure in QList<T>::at: \"index out of range\", file ../../include/QtCore/../../src/corelib/tools/qlist.h, line 393")
    at global/qglobal.cpp:2061
#10 0xb722d42e in qFatal (
    msg=0xb7376aac "ASSERT failure in %s: \"%s\", file %s, line %d")
    at global/qglobal.cpp:2263
#11 0xb722d474 in qt_assert_x (where=0xb6abf974 "QList<T>::at", 
    what=0xb6abf961 "index out of range", 
    file=0xb6abf7e8 "../../include/QtCore/../../src/corelib/tools/qlist.h", 
    line=393) at global/qglobal.cpp:1839
#12 0xb6aae009 in QUndoStack::undoText (this=0x8553110)
    at ../../include/QtCore/../../src/corelib/tools/qlist.h:393
#13 0xb6aae0a4 in QUndoStackPrivate::setIndex (this=0x8581078, idx=17, 
    clean=false) at util/qundostack.cpp:405
#14 0xb6aae47c in QUndoStack::redo (this=0x8553110) at util/qundostack.cpp:689
#15 0xb6abef1b in QUndoStack::qt_metacall (this=0x8553110, 
    _c=QMetaObject::InvokeMetaMethod, _id=9, _a=0xbf8e3a0c)
    at .moc/debug-shared/moc_qundostack.cpp:99
#16 0xb7944db0 in KUndoStack::qt_metacall (this=0x8553110, 
    _c=QMetaObject::InvokeMetaMethod, _id=13, _a=0xbf8e3a0c)
    at /var/tmp/portage/kde-base/kdelibs-4.1.1/work/kdelibs_build/kdeui/kundostack.moc:57
#17 0xb733d131 in QMetaObject::activate (sender=0x84cfb70, 
    from_signal_index=<value optimized out>, to_signal_index=6, 
    argv=0xbf8e3a0c) at kernel/qobject.cpp:3007
#18 0xb733d554 in QMetaObject::activate (sender=0x84cfb70, m=0xb6c76038, 
    from_local_signal_index=1, to_local_signal_index=2, argv=0xbf8e3a0c)
    at kernel/qobject.cpp:3097
#19 0xb64c2f6b in QAction::triggered (this=0x84cfb70, _t1=false)
    at .moc/debug-shared/moc_qaction.cpp:216
#20 0xb64c37dc in QAction::activate (this=0x84cfb70, event=QAction::Trigger)
    at kernel/qaction.cpp:1119
#21 0xb68e9082 in QToolButton::nextCheckState (this=0x6)
    at ../../include/QtGui/../../src/gui/kernel/qaction.h:201
#22 0xb680ffe9 in QAbstractButtonPrivate::click (this=0x86003c0)
    at widgets/qabstractbutton.cpp:526
#23 0xb6810253 in QAbstractButton::mouseReleaseEvent (this=0x8600300, 
    e=0xbf8e412c) at widgets/qabstractbutton.cpp:1116
#24 0xb68e94b6 in QToolButton::mouseReleaseEvent (this=0x8600300, 
    e=0xbf8e412c) at widgets/qtoolbutton.cpp:675
#25 0xb65211ca in QWidget::event (this=0x8600300, event=0xbf8e412c)
    at kernel/qwidget.cpp:7021
#26 0xb680e45c in QAbstractButton::event (this=0x8600300, e=0xbf8e412c)
    at widgets/qabstractbutton.cpp:1078
#27 0xb68e904a in QToolButton::event (this=0x8600300, e=0xbf8e412c)
    at widgets/qtoolbutton.cpp:1105
#28 0xb64c8f1b in QApplicationPrivate::notify_helper (this=0x846cbe8, 
    receiver=0x8600300, e=0xbf8e412c) at kernel/qapplication.cpp:3800
#29 0xb64d03a8 in QApplication::notify (this=0xbf8e47cc, receiver=0x8600300, 
    e=0xbf8e412c) at kernel/qapplication.cpp:3527
#30 0xb78cdce9 in KApplication::notify (this=0xbf8e47cc, receiver=0x8600300, 
    event=0xbf8e412c)
    at /var/tmp/portage/kde-base/kdelibs-4.1.1/work/kdelibs-4.1.1/kdeui/kernel/kapplication.cpp:311
#31 0xb7326771 in QCoreApplication::notifyInternal (this=0xbf8e47cc, 
    receiver=0x8600300, event=0xbf8e412c) at kernel/qcoreapplication.cpp:591
#32 0xb64d17e9 in QApplicationPrivate::sendMouseEvent (receiver=0x8600300, 
    event=0xbf8e412c, alienWidget=0x8600300, nativeWidget=0x85282d0, 
    buttonDown=0xb6c8cc60, lastMouseReceiver=@0xb6c8cc64)
    at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:218
#33 0xb65395d7 in QETWidget::translateMouseEvent (this=0x85282d0, 
    event=0xbf8e4638) at kernel/qapplication_x11.cpp:4048
#34 0xb6537f0e in QApplication::x11ProcessEvent (this=0xbf8e47cc, 
    event=0xbf8e4638) at kernel/qapplication_x11.cpp:3044
#35 0xb655e35d in QEventDispatcherX11::processEvents (this=0x846ccf0, flags=
      {i = -1081194792}) at kernel/qeventdispatcher_x11.cpp:134
#36 0xb7325300 in QEventLoop::processEvents (this=0xbf8e4750, flags=
      {i = -1081194728}) at kernel/qeventloop.cpp:149
#37 0xb73254a2 in QEventLoop::exec (this=0xbf8e4750, flags={i = -1081194664})
    at kernel/qeventloop.cpp:200
#38 0xb73278bf in QCoreApplication::exec () at kernel/qcoreapplication.cpp:849
#39 0xb64c8cb3 in QApplication::exec () at kernel/qapplication.cpp:3330
#40 0x082cef05 in main (argc=1, argv=0xbf8e4924)
    at /var/tmp/portage/kde-base/umbrello-4.1.1/work/umbrello-4.1.1/umbrello/umbrello/main.cpp:110
#0  0xffffe424 in __kernel_vsyscall ()

Still crashes with KDE-4.1.80

Still crashes with KDE-4.2.92

> (note that this will not undo the connection just created) 

This looks like a missing feature in umbrello. While it looks simple to add a QundoCommand based class named CmdCreateAssociation, I do not understand completly how to integrate this class into umbrello.

Following the procedure (using umbrello-4.7.2-3.1.2.x86_64 from OpenSuse 12.1), I get this:

Application: Umbrello UML-modellerer (umbrello), signal: Segmentation fault
[KCrash Handler]
#6  0x00007f034abb2ff7 in QUndoCommand::text() const () from /usr/lib64/libQtGui.so.4
#7  0x00007f034abb33bf in QUndoStack::undoText() const () from /usr/lib64/libQtGui.so.4
#8  0x00007f034abb34aa in ?? () from /usr/lib64/libQtGui.so.4
#9  0x00007f034abd5898 in QUndoStack::qt_metacall(QMetaObject::Call, int, void**) () from /usr/lib64/libQtGui.so.4
#10 0x00007f034a0725aa in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) () from /usr/lib64/libQtCore.so.4
#11 0x00007f034a55b622 in QAction::triggered(bool) () from /usr/lib64/libQtGui.so.4
#12 0x00007f034a55b80f in QAction::activate(QAction::ActionEvent) () from /usr/lib64/libQtGui.so.4
#13 0x00007f034a55b97f in QAction::event(QEvent*) () from /usr/lib64/libQtGui.so.4
#14 0x00007f034a561c34 in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib64/libQtGui.so.4
#15 0x00007f034a566ac1 in QApplication::notify(QObject*, QEvent*) () from /usr/lib64/libQtGui.so.4
#16 0x00007f034b9a9e36 in KApplication::notify (this=0x7fff5b73fdd0, receiver=0xc220f0, event=0x7fff5b73e8f0) at /usr/src/debug/kdelibs-4.7.2/kdeui/kernel/kapplication.cpp:311
#17 0x00007f034a05f82c in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib64/libQtCore.so.4
#18 0x00007f034a593c19 in ?? () from /usr/lib64/libQtGui.so.4
#19 0x00007f034a59510d in ?? () from /usr/lib64/libQtGui.so.4
#20 0x00007f034a568729 in QApplication::notify(QObject*, QEvent*) () from /usr/lib64/libQtGui.so.4
#21 0x00007f034b9a9e36 in KApplication::notify (this=0x7fff5b73fdd0, receiver=0xc62510, event=0x7fff5b73ee90) at /usr/src/debug/kdelibs-4.7.2/kdeui/kernel/kapplication.cpp:311
#22 0x00007f034a05f82c in QCoreApplication::notifyInternal(QObject*, QEvent*) () from /usr/lib64/libQtCore.so.4
#23 0x00007f034a600f79 in ?? () from /usr/lib64/libQtGui.so.4
#24 0x00007f034a6013eb in ?? () from /usr/lib64/libQtGui.so.4
#25 0x00007f034a5dd5d4 in QApplication::x11ProcessEvent(_XEvent*) () from /usr/lib64/libQtGui.so.4
#26 0x00007f034a605312 in ?? () from /usr/lib64/libQtGui.so.4
#27 0x00007f03452d158d in g_main_dispatch (context=0xb030e0) at gmain.c:2425
#28 g_main_context_dispatch (context=0xb030e0) at gmain.c:2995
#29 0x00007f03452d1d88 in g_main_context_iterate (context=0xb030e0, block=<optimized out>, dispatch=1, self=<optimized out>) at gmain.c:3073
#30 0x00007f03452d1f59 in g_main_context_iteration (context=0xb030e0, may_block=1) at gmain.c:3136
#31 0x00007f034a08a51f in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib64/libQtCore.so.4
#32 0x00007f034a604f9e in ?? () from /usr/lib64/libQtGui.so.4
#33 0x00007f034a05ea32 in QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib64/libQtCore.so.4
#34 0x00007f034a05ec2f in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib64/libQtCore.so.4
#35 0x00007f034a062df7 in QCoreApplication::exec() () from /usr/lib64/libQtCore.so.4
#36 0x000000000043d966 in main (argc=3, argv=0x7fff5b7401d8) at /usr/src/debug/kdesdk-4.7.2/umbrello/umbrello/main.cpp:111

There is a (simpler) way to reproduce, see bug 240606.

*** Bug 249189 has been marked as a duplicate of this bug. ***

*** Bug 207690 has been marked as a duplicate of this bug. ***

*** This bug has been marked as a duplicate of bug 306830 ***