Version:            (using KDE 4.1.3)
Compiler:          gcc-4.3.2 
OS:                Linux
Installed from:    Gentoo Packages

I did not actively trigger a delete event (although the backtrace might suggest so), the machine was unattended when the process crashed.

Backtrace:
Application: Kontact (kontact), signal SIGABRT
Using host libthread_db library "/lib/libthread_db.so.1".
[Thread debugging using libthread_db enabled]
[New Thread 0xb50436d0 (LWP 22889)]
[KCrash handler]
#6  0xb807b424 in __kernel_vsyscall ()
#7  0xb5472c20 in raise () from /lib/libc.so.6
#8  0xb5474478 in abort () from /lib/libc.so.6
#9  0xb7e83fbd in qt_message_output (msgType=QtFatalMsg, 
    buf=0xbff935f0 "ASSERT: \"node->mToDelete\" in file /var/tmp/portage/kde-base/korganizer-4.1.3/work/korganizer-4.1.3/korganizer/views/todoview/kotodomodel.cpp, line 112") at global/qglobal.cpp:2108
#10 0xb7e84086 in qFatal (msg=0xb7fe0f9c "ASSERT: \"%s\" in file %s, line %d")
    at global/qglobal.cpp:2309
#11 0xb7e84405 in qt_assert (assertion=0xb1815a79 "node->mToDelete", 
    file=0xb18157d8 "/var/tmp/portage/kde-base/korganizer-4.1.3/work/korganizer-4.1.3/korganizer/views/todoview/kotodomodel.cpp", line=112)
    at global/qglobal.cpp:1878
#12 0xb1738132 in KOTodoModel::TodoTreeNode::deleteMarked (this=0x9c84598)
    at /var/tmp/portage/kde-base/korganizer-4.1.3/work/korganizer-4.1.3/korganizer/views/todoview/kotodomodel.cpp:112
#13 0xb1738268 in KOTodoModel::TodoTreeNode::deleteMarked (this=0x9bc7dc0)
    at /var/tmp/portage/kde-base/korganizer-4.1.3/work/korganizer-4.1.3/korganizer/views/todoview/kotodomodel.cpp:126
#14 0xb1735d34 in KOTodoModel::reloadTodos (this=0x9bc0b10)
    at /var/tmp/portage/kde-base/korganizer-4.1.3/work/korganizer-4.1.3/korganizer/views/todoview/kotodomodel.cpp:249
#15 0xb173db20 in KOTodoView::updateView (this=0x9bb3848)
    at /var/tmp/portage/kde-base/korganizer-4.1.3/work/korganizer-4.1.3/korganizer/views/todoview/kotodoview.cpp:311
#16 0xb174cb38 in CalendarView::updateView (this=0x8e4fa08, 
    start=@0x1c226a74, end=@0x1c226a74)
    at /var/tmp/portage/kde-base/korganizer-4.1.3/work/korganizer-4.1.3/korganizer/calendarview.cpp:779
#17 0xb174cc47 in CalendarView::updateView (this=0x8e4fa08)
    at /var/tmp/portage/kde-base/korganizer-4.1.3/work/korganizer-4.1.3/korganizer/calendarview.cpp:789
#18 0xb1747e49 in CalendarView::slotCalendarChanged (this=0x8e4fa08)
    at /var/tmp/portage/kde-base/korganizer-4.1.3/work/korganizer-4.1.3/korganizer/calendarview.cpp:2223
#19 0xb1751f70 in CalendarView::qt_metacall (this=0x8e4fa08, 
    _c=QMetaObject::InvokeMetaMethod, _id=165, _a=0xbff959c8)
    at /var/tmp/portage/kde-base/korganizer-4.1.3/work/korganizer_build/korganizer/calendarview.moc:557
#20 0xb7fa3f39 in QMetaObject::activate (sender=0x9bf13f8, 
    from_signal_index=<value optimized out>, to_signal_index=4, argv=0x0)
    at kernel/qobject.cpp:3028
#21 0xb7fa5ee2 in QMetaObject::activate (sender=0x9bf13f8, m=0xb6505e0c, 
    local_signal_index=0, argv=0x0) at kernel/qobject.cpp:3098
#22 0xb648de27 in KCal::Calendar::calendarChanged (this=0x9bf13f8)
    at /var/tmp/portage/kde-base/kdepimlibs-4.1.3/work/kdepimlibs_build/kcal/calendar.moc:84
#23 0xb648de95 in KCal::Calendar::qt_metacall (this=0x9bf13f8, 
    _c=QMetaObject::InvokeMetaMethod, _id=0, _a=0xbff95b4c)
    at /var/tmp/portage/kde-base/kdepimlibs-4.1.3/work/kdepimlibs_build/kcal/calendar.moc:72
#24 0xb64dc34a in KCal::CalendarResources::qt_metacall (this=0x9bf13f8, 
    _c=QMetaObject::InvokeMetaMethod, _id=4, _a=0xbff95b4c)
    at /var/tmp/portage/kde-base/kdepimlibs-4.1.3/work/kdepimlibs_build/kcal/calendarresources.moc:75
#25 0xb7fa3f39 in QMetaObject::activate (sender=0x9bf2fc8, 
    from_signal_index=<value optimized out>, to_signal_index=4, 
    argv=0xbff95b4c) at kernel/qobject.cpp:3028
#26 0xb7fa5ee2 in QMetaObject::activate (sender=0x9bf2fc8, m=0xb6506794, 
    local_signal_index=0, argv=0xbff95b4c) at kernel/qobject.cpp:3098
#27 0xb64ccf23 in KCal::ResourceCalendar::resourceChanged (this=0x9bf2fc8, 
    _t1=0x9bf2fc8)
    at /var/tmp/portage/kde-base/kdepimlibs-4.1.3/work/kdepimlibs_build/kcal/resourcecalendar.moc:115
#28 0xb12c9cea in KCal::ResourceKolab::slotEmitResourceChanged (
    this=0x9bf2fc8)
    at /var/tmp/portage/kde-base/kdepim-kresources-4.1.3/work/kdepim-kresources-4.1.3/kresources/kolab/kcal/resourcekolab.cpp:1094
#29 0xb12c9d7d in KCal::ResourceKolab::qt_metacall (this=0x9bf2fc8, 
    _c=QMetaObject::InvokeMetaMethod, _id=1, _a=0xbff95c58)
    at /var/tmp/portage/kde-base/kdepim-kresources-4.1.3/work/kdepim-kresources_build/kresources/kolab/kcal/resourcekolab.moc:76
#30 0xb7fa3f39 in QMetaObject::activate (sender=0x9bf3028, 
    from_signal_index=<value optimized out>, to_signal_index=4, argv=0x0)
    at kernel/qobject.cpp:3028
#31 0xb7fa5ee2 in QMetaObject::activate (sender=0x9bf3028, m=0xb80779c4, 
    local_signal_index=0, argv=0x0) at kernel/qobject.cpp:3098
#32 0xb7fe02c7 in QTimer::timeout (this=0x9bf3028)
    at .moc/debug-shared/moc_qtimer.cpp:126
#33 0xb7faa71e in QTimer::timerEvent (this=0x9bf3028, e=0xbff960ec)
    at kernel/qtimer.cpp:263
#34 0xb7f9cf2f in QObject::event (this=0x9bf3028, e=0xbff960ec)
    at kernel/qobject.cpp:1117
#35 0xb5a0694c in QApplicationPrivate::notify_helper (this=0x899d1d0, 
    receiver=0x9bf3028, e=0xbff960ec) at kernel/qapplication.cpp:3809
#36 0xb5a0db1f in QApplication::notify (this=0xbff96488, receiver=0x9bf3028, 
    e=0xbff960ec) at kernel/qapplication.cpp:3399
#37 0xb7ad26b1 in KApplication::notify (this=0xbff96488, receiver=0x9bf3028, 
    event=0xbff960ec)
    at /var/tmp/portage/kde-base/kdelibs-4.1.3-r1/work/kdelibs-4.1.3/kdeui/kernel/kapplication.cpp:311
#38 0xb7f8bebf in QCoreApplication::notifyInternal (this=0xbff96488, 
    receiver=0x9bf3028, event=0xbff960ec) at kernel/qcoreapplication.cpp:593
#39 0xb7fbb6a1 in QTimerInfoList::activateTimers (this=0x899d91c)
    at kernel/qcoreapplication.h:215
#40 0xb7fbb89b in QEventDispatcherUNIX::processEvents (this=0x899c2b0, flags=
      {i = -1074175124}) at kernel/qeventdispatcher_unix.cpp:899
#41 0xb5aa4fe6 in QEventDispatcherX11::processEvents (this=0x899c2b0, flags=
      {i = -1074175064}) at kernel/qeventdispatcher_x11.cpp:154
#42 0xb7f8a82a in QEventLoop::processEvents (this=0xbff96420, flags=
      {i = -1074175000}) at kernel/qeventloop.cpp:149
#43 0xb7f8a9ea in QEventLoop::exec (this=0xbff96420, flags={i = -1074174936})
    at kernel/qeventloop.cpp:200
#44 0xb7f8d155 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:851
#45 0xb5a06677 in QApplication::exec () at kernel/qapplication.cpp:3337
#46 0x0804b92d in main (argc=1, argv=0xbff96644)
    at /var/tmp/portage/kde-base/kontact-4.1.3/work/kontact-4.1.3/kontact/src/main.cpp:218
#0  0xb807b424 in __kernel_vsyscall ()