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

I've edited an recurring event and then clicked 'OK', as I remember.
And Kontact has crashed.
It is HEAD, 28 Jan.

The trace:
[New Thread 1024 (LWP 25995)]
0x41625fe9 in wait4 () from /lib/libc.so.6
#0  0x41625fe9 in wait4 () from /lib/libc.so.6
#1  0x4169fc4c in sys_sigabbrev () from /lib/libc.so.6
#2  0x4149aa43 in waitpid () from /lib/libpthread.so.0
#3  0x40924ad7 in KCrash::defaultCrashHandler(int) ()
   from /mnt/devspace/kde/lib/libkdecore.so.4
#4  0x4149810b in pthread_sighandler () from /lib/libpthread.so.0
#5  0x415b3108 in sigaction () from /lib/libc.so.6
#6  0x42c73bd3 in KOIncidenceEditor::slotOk() ()
   from /mnt/devspace/kde/lib/libkorganizer.so.1
#7  0x406ccf84 in KDialogBase::qt_invoke(int, QUObject*) ()
   from /mnt/devspace/kde/lib/libkdeui.so.4
#8  0x42c74d4c in KOIncidenceEditor::qt_invoke(int, QUObject*) ()
   from /mnt/devspace/kde/lib/libkorganizer.so.1
#9  0x42c77177 in KOEventEditor::qt_invoke(int, QUObject*) ()
   from /mnt/devspace/kde/lib/libkorganizer.so.1
#10 0x40d71963 in QObject::activate_signal(QConnectionList*, QUObject*) (
    this=0x99c64f8, clist=0x9cebbe0, o=0xbfffed00) at kernel/qobject.cpp:2333
#11 0x40d71802 in QObject::activate_signal(int) (this=0x99c64f8, signal=4)
    at kernel/qobject.cpp:2302
#12 0x410bc131 in QButton::clicked() (this=0x99c64f8)
    at .moc/debug-shared-mt/moc_qbutton.cpp:152
#13 0x40e052b7 in QButton::mouseReleaseEvent(QMouseEvent*) (this=0x99c64f8, 
    e=0xbffff090) at widgets/qbutton.cpp:820
#14 0x40da8cfd in QWidget::event(QEvent*) (this=0x99c64f8, e=0xbffff090)
    at kernel/qwidget.cpp:4426
#15 0x40d0ef51 in QApplication::internalNotify(QObject*, QEvent*) (
    this=0xbffff4b0, receiver=0x99c64f8, e=0xbffff090)
    at kernel/qapplication.cpp:2582
#16 0x40d0e707 in QApplication::notify(QObject*, QEvent*) (this=0xbffff4b0, 
    receiver=0x99c64f8, e=0xbffff090) at kernel/qapplication.cpp:2368
#17 0x4088bbf1 in KApplication::notify(QObject*, QEvent*) ()
   from /mnt/devspace/kde/lib/libkdecore.so.4
#18 0x40ca4e8b in QApplication::sendSpontaneousEvent(QObject*, QEvent*) (
    receiver=0x99c64f8, event=0xbffff090) at qapplication.h:495
#19 0x40c9e6ab in QETWidget::translateMouseEvent(_XEvent const*) (
    this=0x99c64f8, event=0xbffff3a0) at kernel/qapplication_x11.cpp:4351
#20 0x40c9c3ef in QApplication::x11ProcessEvent(_XEvent*) (this=0xbffff4b0, 
    event=0xbffff3a0) at kernel/qapplication_x11.cpp:3529
#21 0x40cb603a in QEventLoop::processEvents(unsigned) (this=0x80c5610, flags=4)
    at kernel/qeventloop_x11.cpp:192
#22 0x40d248d2 in QEventLoop::enterLoop() (this=0x80c5610)
    at kernel/qeventloop.cpp:198
#23 0x40d247ee in QEventLoop::exec() (this=0x80c5610)
    at kernel/qeventloop.cpp:145
#24 0x40d0f0d5 in QApplication::exec() (this=0xbffff4b0)
    at kernel/qapplication.cpp:2705
#25 0x08058802 in main ()
#26 0x415a2652 in __libc_start_main () from /lib/libc.so.6