Version:           1.9.51 (using 4.00.80 (KDE 4.0.80 >= (KDE 4.1 Beta1), compiled sources)
Compiler:          gcc
OS:                Linux (i686) release 2.6.24-gentoo-r8

Steps to reproduce:

1) Open Kmail (needs to be done via kontact. I cannot reproduce this with the kmail standalone app)
2) Switch from long folder list to short folder list [Configure KMail -> Appearance -> Layout -> Short folder list] (works vice versa too)
3) Close kontact and see it crash with the following backtrace (kdepimlibs r812282 and kdepim r812462)

Remark: The backtrace I get looks very similar to the backtraces of bug #160920 and bug #102470. However, as I end up with this backtrace via a completely differnt set of actions, I post this in a new bugreport.

Application: Kontact (kontact), signal SIGSEGV
Using host libthread_db library "/lib/libthread_db.so.1".
[Thread debugging using libthread_db enabled]
[New Thread 0xb4ae36f0 (LWP 32087)]
[KCrash handler]
#6  0xb6c6caa3 in ?? () from /usr/lib/qt4/libQtGui.so.4
#7  0xb6c5a3e1 in QWidget::removeAction () from /usr/lib/qt4/libQtGui.so.4
#8  0xb7ad5d1f in KXMLGUI::ActionList::unplug (this=0x873ba14, 
    container=0x8723290)
    at /home/kde-devel/kde/src/KDE/kdelibs/kdeui/xmlgui/kxmlguifactory_p.cpp:52
#9  0xb7ad5ee5 in KXMLGUI::ContainerNode::unplugClient (this=0x873b9a8, 
    client=0x873ba10)
    at /home/kde-devel/kde/src/KDE/kdelibs/kdeui/xmlgui/kxmlguifactory_p.cpp:438
#10 0xb7ad611f in KXMLGUI::ContainerNode::unplugActions (this=0x873b9a8, 
    state=@0x8227640)
    at /home/kde-devel/kde/src/KDE/kdelibs/kdeui/xmlgui/kxmlguifactory_p.cpp:417
#11 0xb7ad61c7 in KXMLGUI::ContainerNode::destruct (this=0x873b9a8, 
    element=@0xbfce1e4c, state=@0x8227640)
    at /home/kde-devel/kde/src/KDE/kdelibs/kdeui/xmlgui/kxmlguifactory_p.cpp:326
#12 0xb7ad63cf in KXMLGUI::ContainerNode::destructChildren (this=0x822bcc8, 
    element=@0xbfce1ecc, state=@0x8227640)
    at /home/kde-devel/kde/src/KDE/kdelibs/kdeui/xmlgui/kxmlguifactory_p.cpp:369
#13 0xb7ad61b5 in KXMLGUI::ContainerNode::destruct (this=0x822bcc8, 
    element=@0xbfce1ecc, state=@0x8227640)
    at /home/kde-devel/kde/src/KDE/kdelibs/kdeui/xmlgui/kxmlguifactory_p.cpp:324
#14 0xb7ad63cf in KXMLGUI::ContainerNode::destructChildren (this=0x8227870, 
    element=@0xbfce1f88, state=@0x8227640)
    at /home/kde-devel/kde/src/KDE/kdelibs/kdeui/xmlgui/kxmlguifactory_p.cpp:369
#15 0xb7ad61b5 in KXMLGUI::ContainerNode::destruct (this=0x8227870, 
    element=@0xbfce1f88, state=@0x8227640)
    at /home/kde-devel/kde/src/KDE/kdelibs/kdeui/xmlgui/kxmlguifactory_p.cpp:324
#16 0xb7ad079b in KXMLGUIFactory::removeClient (this=0x8228480, 
    client=0x82d6204)
    at /home/kde-devel/kde/src/KDE/kdelibs/kdeui/xmlgui/kxmlguifactory.cpp:337
#17 0xb759ce5d in KParts::MainWindow::createGUI (this=0x80a60d8, part=0x0)
    at /home/kde-devel/kde/src/KDE/kdelibs/kparts/mainwindow.cpp:106
#18 0xb60274e7 in ~MainWindow (this=0x80a60d8)
    at /home/kde-devel/kde/src/KDE/kdepim/kontact/src/mainwindow.cpp:236
#19 0xb7ea52b2 in qDeleteInEventHandler () from /usr/lib/qt4/libQtCore.so.4
#20 0xb7ea72ca in QObject::event () from /usr/lib/qt4/libQtCore.so.4
#21 0xb6c6b434 in QWidget::event () from /usr/lib/qt4/libQtGui.so.4
#22 0xb6fde05e in QMainWindow::event () from /usr/lib/qt4/libQtGui.so.4
#23 0xb7a8697f in KMainWindow::event (this=0x80a60d8, ev=0x84fb3b8)
    at /home/kde-devel/kde/src/KDE/kdelibs/kdeui/widgets/kmainwindow.cpp:1002
#24 0xb7ac6abf in KXmlGuiWindow::event (this=0x80a60d8, ev=0x84fb3b8)
    at /home/kde-devel/kde/src/KDE/kdelibs/kdeui/xmlgui/kxmlguiwindow.cpp:122
#25 0xb6c128a4 in QApplicationPrivate::notify_helper ()
   from /usr/lib/qt4/libQtGui.so.4
#26 0xb6c169b2 in QApplication::notify () from /usr/lib/qt4/libQtGui.so.4
#27 0xb79c1be6 in KApplication::notify (this=0xbfce27dc, receiver=0x80a60d8, 
    event=0x84fb3b8)
    at /home/kde-devel/kde/src/KDE/kdelibs/kdeui/kernel/kapplication.cpp:311
#28 0xb7e95d59 in QCoreApplication::notifyInternal ()
   from /usr/lib/qt4/libQtCore.so.4
#29 0xb7e97006 in QCoreApplicationPrivate::sendPostedEvents ()
   from /usr/lib/qt4/libQtCore.so.4
#30 0xb7e9735d in QCoreApplication::sendPostedEvents ()
   from /usr/lib/qt4/libQtCore.so.4
#31 0xb7e97431 in QCoreApplication::exec () from /usr/lib/qt4/libQtCore.so.4
#32 0xb6c1223f in QApplication::exec () from /usr/lib/qt4/libQtGui.so.4
#33 0x0804b2d9 in main (argc=134570264, argv=0x8056148)
    at /home/kde-devel/kde/src/KDE/kdepim/kontact/src/main.cpp:174
#0  0xb7f85410 in __kernel_vsyscall ()