Version:            (using KDE KDE 3.3.2)
Installed from:    SuSE RPMs

I moved around a large number of mails between folders and subfolders. The idea was to create an archive of my messages so far. I created a folder named "archive" and duplicated the original folder structure, as there is no way to drag+drop/move complete subfolders between folders. 

The next step was marking all messages in a subfolder (CTRL+A) and then drag+drop them to their new destination. The first step works fine, but on the second folder I try to move, KMail crashes. None of the messages get lost, however, on the next start, they are in their original location. This resembles my folder structure:

*--Inbox
 |-Outbox
 |-Trash
 |-Folder A
 | |-Subfolder 1
 | |-Subfolder 2
 |-Folder B
   |-Subfolder 1
   |-Subfolder 2

I tried to move message from, say, A.1 to B.2, and KMail crashed. Here's the backtrace:

Using host libthread_db library "/lib/tls/libthread_db.so.1".
[Thread debugging using libthread_db enabled]
[New Thread 1099198432 (LWP 8322)]
[KCrash handler]
#7  0x4121d74e in QGDict::look_string () from /usr/lib/qt3/lib/libqt-mt.so.3
#8  0x420c9a5a in KMHeaders::msgRemoved ()
   from /opt/kde3/lib/libkmailprivate.so.0
#9  0x420ca1e9 in KMHeaders::qt_invoke ()
   from /opt/kde3/lib/libkmailprivate.so.0
#10 0x40f5631e in QObject::activate_signal ()
   from /usr/lib/qt3/lib/libqt-mt.so.3
#11 0x41f8d032 in KMFolder::msgRemoved ()
   from /opt/kde3/lib/libkmailprivate.so.0
#12 0x41fd4ebb in KMFolder::qt_emit () from /opt/kde3/lib/libkmailprivate.so.0
#13 0x40f56351 in QObject::activate_signal ()
   from /usr/lib/qt3/lib/libqt-mt.so.3
#14 0x41f8c972 in FolderStorage::msgRemoved ()
   from /opt/kde3/lib/libkmailprivate.so.0
#15 0x4207d190 in FolderStorage::take ()
   from /opt/kde3/lib/libkmailprivate.so.0
#16 0x42088d52 in KMFolderMaildir::take ()
   from /opt/kde3/lib/libkmailprivate.so.0
#17 0x41f26111 in KMFolder::take () from /opt/kde3/lib/libkmailprivate.so.0
#18 0x4215b716 in KMFolderMaildir::addMsg ()
   from /opt/kde3/lib/libkmailprivate.so.0
#19 0x41f27093 in FolderStorage::moveMsg ()
   from /opt/kde3/lib/libkmailprivate.so.0
#20 0x41f26238 in KMFolder::moveMsg () from /opt/kde3/lib/libkmailprivate.so.0
#21 0x4201f307 in KMMoveCommand::execute ()
   from /opt/kde3/lib/libkmailprivate.so.0
#22 0x42016f49 in KMCommand::slotPostTransfer ()
   from /opt/kde3/lib/libkmailprivate.so.0
#23 0x42017007 in KMCommand::qt_invoke ()
   from /opt/kde3/lib/libkmailprivate.so.0
#24 0x420172fb in KMMenuCommand::qt_invoke ()
   from /opt/kde3/lib/libkmailprivate.so.0
#25 0x42017361 in KMMoveCommand::qt_invoke ()
   from /opt/kde3/lib/libkmailprivate.so.0
#26 0x40f5631e in QObject::activate_signal ()
   from /usr/lib/qt3/lib/libqt-mt.so.3
#27 0x41f653b2 in KMCommand::messagesTransfered ()
   from /opt/kde3/lib/libkmailprivate.so.0
#28 0x41fe1c3a in KMCommand::transferSelectedMsgs ()
   from /opt/kde3/lib/libkmailprivate.so.0
#29 0x41fe225b in KMCommand::slotStart ()
   from /opt/kde3/lib/libkmailprivate.so.0
#30 0x42017014 in KMCommand::qt_invoke ()
   from /opt/kde3/lib/libkmailprivate.so.0
#31 0x420172fb in KMMenuCommand::qt_invoke ()
   from /opt/kde3/lib/libkmailprivate.so.0
#32 0x42017361 in KMMoveCommand::qt_invoke ()
   from /opt/kde3/lib/libkmailprivate.so.0
#33 0x40f5631e in QObject::activate_signal ()
   from /usr/lib/qt3/lib/libqt-mt.so.3
#34 0x412a8132 in QSignal::signal () from /usr/lib/qt3/lib/libqt-mt.so.3
#35 0x40f73873 in QSignal::activate () from /usr/lib/qt3/lib/libqt-mt.so.3
#36 0x40f7b2c3 in QSingleShotTimer::event ()
   from /usr/lib/qt3/lib/libqt-mt.so.3
#37 0x40ef3baf in QApplication::internalNotify ()
   from /usr/lib/qt3/lib/libqt-mt.so.3
#38 0x40ef5773 in QApplication::notify () from /usr/lib/qt3/lib/libqt-mt.so.3
#39 0x40b84e21 in KApplication::notify () from /opt/kde3/lib/libkdecore.so.4
#40 0x40ee835c in QEventLoop::activateTimers ()
   from /usr/lib/qt3/lib/libqt-mt.so.3
#41 0x40ea1156 in QEventLoop::processEvents ()
   from /usr/lib/qt3/lib/libqt-mt.so.3
#42 0x40f0bb41 in QEventLoop::enterLoop () from /usr/lib/qt3/lib/libqt-mt.so.3
#43 0x40f0b986 in QEventLoop::exec () from /usr/lib/qt3/lib/libqt-mt.so.3
#44 0x40ef563f in QApplication::exec () from /usr/lib/qt3/lib/libqt-mt.so.3
#45 0x08063d87 in main ()

Hope this helps. Greetings, Gunnar :)