Kmail/Kontact crashes when opening a folder for the first time using option 'go to last selected message'

Yesterday and the day before, i was configurating Kontact (esp. KMail in there) to migrate from Thunderbird. After I set up my email accounts, i found and selected the option to go to the last selected message when opening a folder.
From then on, KMail was crashing instantly when opening a folder for the first time, but also when deleting an message (as i remember right now).

Kubuntu 7.04 Feisty Fawn
KMail 1.9.6
Kontact 1.2.4

Got a backtrace:

Using host libthread_db library "/lib/tls/i686/cmov/libthread_db.so.1".
[Thread debugging using libthread_db enabled]
[New Thread -1242621728 (LWP 7269)]
[New Thread -1286493296 (LWP 7273)]
[New Thread -1278100592 (LWP 7272)]
[New Thread -1269707888 (LWP 7271)]
[New Thread -1261315184 (LWP 7270)]
[KCrash handler]
#6 0xb72e54c1 in QGDict::look_string () from /usr/lib/libqt-mt.so.3
#7 0xb51e3c15 in KMHeaders::writeSortOrder ()
   from /usr/lib/libkmailprivate.so
#8 0xb51e46ae in KMHeaders::setFolder () from /usr/lib/libkmailprivate.so
#9 0xb522f6e6 in KMMainWidget::folderSelected ()
   from /usr/lib/libkmailprivate.so
#10 0xb5272897 in KMMainWidget::qt_invoke () from /usr/lib/libkmailprivate.so
#11 0xb6feb9b8 in QObject::activate_signal () from /usr/lib/libqt-mt.so.3
#12 0xb4fd4aee in KMFolderTree::folderSelected ()
   from /usr/lib/libkmailprivate.so
#13 0xb51bc852 in KMFolderTree::doFolderSelected ()
   from /usr/lib/libkmailprivate.so
#14 0xb51bcdc1 in KMFolderTree::contentsMouseReleaseEvent ()
   from /usr/lib/libkmailprivate.so
#15 0xb7120f17 in QScrollView::viewportMouseReleaseEvent ()
   from /usr/lib/libqt-mt.so.3
#16 0xb71224ae in QScrollView::eventFilter () from /usr/lib/libqt-mt.so.3
#17 0xb70ea75e in QListView::eventFilter () from /usr/lib/libqt-mt.so.3
#18 0xb4fb97a9 in KMFolderTree::eventFilter ()
   from /usr/lib/libkmailprivate.so
#19 0xb6feae38 in QObject::activate_filters () from /usr/lib/libqt-mt.so.3
#20 0xb6feaeb6 in QObject::event () from /usr/lib/libqt-mt.so.3
#21 0xb702258f in QWidget::event () from /usr/lib/libqt-mt.so.3
#22 0xb6f82a60 in QApplication::internalNotify () from /usr/lib/libqt-mt.so.3
#23 0xb6f84c1e in QApplication::notify () from /usr/lib/libqt-mt.so.3
#24 0xb76bfce2 in KApplication::notify () from /usr/lib/libkdecore.so.4
#25 0xb6f1525d in QApplication::sendSpontaneousEvent ()
   from /usr/lib/libqt-mt.so.3
#26 0xb6f13ec2 in QETWidget::translateMouseEvent ()
   from /usr/lib/libqt-mt.so.3
#27 0xb6f11fac in QApplication::x11ProcessEvent () from /usr/lib/libqt-mt.so.3
#28 0xb6f29180 in QEventLoop::processEvents () from /usr/lib/libqt-mt.so.3
#29 0xb6f9d136 in QEventLoop::enterLoop () from /usr/lib/libqt-mt.so.3
#30 0xb6f9cf46 in QEventLoop::exec () from /usr/lib/libqt-mt.so.3
#31 0xb6f84609 in QApplication::exec () from /usr/lib/libqt-mt.so.3
#32 0x08061e25 in ?? ()
#33 0xbfd3a6ac in ?? ()
#34 0x00000001 in ?? ()
#35 0x00000001 in ?? ()
#36 0x00000000 in ?? ()