Version:           1.9.5 (using KDE KDE 3.5.5)
Installed from:    Gentoo Packages
Compiler:          gcc 4.1.1 
OS:                Linux

In a folder on a remote IMAP server, I entered the folder and tried to delete all of the 7 messages in there (2 of which were new/unread). 
Ctrl-A to select all messages, DEL to delete. Kmail crashed.
Deleting each message individually worked without problem so no one mail seems to be to blame.
(Remote server is Microsoft Exchange Server 2003 IMAP4rev1 server version 6.5.7638.1).

Last few lines of debug output (some information replaced with XXXX)

kontact: processNewMail true,status=1
kmail: KMFolderImap::checkValidity of: /INBOX/XXXX/lists/XXXX/cvs/
kmail: slotCheckNamespace - Admin Contacts,Michaels Contacts
kmail: delimiterForNamespace Public Folders
kmail: found namespace folder Public Folders
kmail: capabilities:(imap4,imap4rev1,idle,login-referrals,mailbox-referrals,namespace,literal+,uidplus,children,auth=ntlm)
kmail: KMFolderImap::slotCheckValidityResult of: cvs
kmail: connections to server XXXX now 0
kmail: processNextCheck, remaining 0
kmail: account XXXX finished check
kmail: 2 new message(s) in .1944288694.directory/.INBOX.directory/.XXXX.directory/.lists.directory/.XXXX.directory/cvs
kmail: ImapJob::slotGetMessageResult - retrieved part HEADER
kmail: (21157, last 0) XXXX, readyToShow false
kmail: [const QTextCodec* KMReaderWin::overrideCodec() const]  mOverrideEncoding == ''
kmail: ImapAccountBase::constructParts - created id 0 of type MULTIPART/MIXED
kmail: ImapAccountBase::constructParts - created id 1 of type MULTIPART/ALTERNATIVE
kmail: ImapAccountBase::constructParts - created id 1.1 of type TEXT/PLAIN
kmail: ImapAccountBase::constructParts - created id 1.2 of type TEXT/HTML
kmail: ImapAccountBase::constructParts - created id 2 of type TEXT/PLAIN
kmail: Falling back to normal mode
kontact: folderstorage.cpp:583: virtual int FolderStorage::moveMsg(KMMessage*, int*): Assertion `aMsg != 0' failed.
*** KMail got signal 6 (Crashing)
KCrash: Application 'kontact' crashing...


Kcrash backtrace:
[KCrash handler]
#6  0xffffe410 in __kernel_vsyscall ()
#7  0xb620e601 in raise () from /lib/libc.so.6
#8  0xb620fc69 in abort () from /lib/libc.so.6
#9  0xb6207eac in __assert_fail () from /lib/libc.so.6
#10 0xb5b153ec in FolderStorage::moveMsg (this=0x8463700, aMsg=0x0, 
    aIndex_ret=0xbffedad0) at folderstorage.cpp:583
#11 0xb5aff69c in KMFolder::moveMsg (this=0x8463220, msg=0x0, 
    index_return=0xbffedad0) at kmfolder.cpp:419
#12 0xb5bd9263 in KMMoveCommand::execute (this=0x864a140)
    at kmcommands.cpp:1956
#13 0xb5be019f in KMCommand::slotPostTransfer (this=0x864a140, 
    result=KMCommand::OK) at kmcommands.cpp:256
#14 0xb5be03f4 in KMCommand::qt_invoke (this=0x864a140, _id=5, _o=0xbffedbf8)
    at kmcommands.moc:148
#15 0xb5be0743 in KMMenuCommand::qt_invoke (this=0x864a140, _id=5, 
    _o=0xbffedbf8) at kmcommands.moc:2509
#16 0xb5be0800 in KMMoveCommand::qt_invoke (this=0x864a140, _id=5, 
    _o=0xbffedbf8) at kmcommands.moc:2692
#17 0xb5be082b in KMDeleteMsgCommand::qt_invoke (this=0x864a140, _id=5, 
    _o=0xbffedbf8) at kmcommands.moc:2767
#18 0xb68f7859 in QObject::activate_signal () from /usr/qt/3/lib/libqt-mt.so.3
#19 0xb5bd48ba in KMCommand::messagesTransfered (this=0x864a140, 
    t0=KMCommand::OK) at kmcommands.moc:126
#20 0xb5be0104 in KMCommand::transferSelectedMsgs (this=0x864a140)
    at kmcommands.cpp:351
#21 0xb5be0304 in KMCommand::slotStart (this=0x864a140) at kmcommands.cpp:248
#22 0xb5be03ce in KMCommand::qt_invoke (this=0x864a140, _id=4, _o=0xbffedd70)
    at kmcommands.moc:147
#23 0xb5be0743 in KMMenuCommand::qt_invoke (this=0x864a140, _id=4, 
    _o=0xbffedd70) at kmcommands.moc:2509
#24 0xb5be0800 in KMMoveCommand::qt_invoke (this=0x864a140, _id=4, 
    _o=0xbffedd70) at kmcommands.moc:2692
#25 0xb5be082b in KMDeleteMsgCommand::qt_invoke (this=0x864a140, _id=4, 
    _o=0xbffedd70) at kmcommands.moc:2767
#26 0xb68f7859 in QObject::activate_signal () from /usr/qt/3/lib/libqt-mt.so.3
#27 0xb6c303fe in QSignal::signal () from /usr/qt/3/lib/libqt-mt.so.3
#28 0xb6913815 in QSignal::activate () from /usr/qt/3/lib/libqt-mt.so.3
#29 0xb691ac73 in QSingleShotTimer::event () from /usr/qt/3/lib/libqt-mt.so.3
#30 0xb6898687 in QApplication::internalNotify ()
   from /usr/qt/3/lib/libqt-mt.so.3
#31 0xb6899241 in QApplication::notify () from /usr/qt/3/lib/libqt-mt.so.3
#32 0xb6ee55be in KApplication::notify ()
   from /usr/kde/3.5/lib/libkdecore.so.4
#33 0xb688d81c in QEventLoop::activateTimers ()
   from /usr/qt/3/lib/libqt-mt.so.3
#34 0xb684883c in QEventLoop::processEvents ()
   from /usr/qt/3/lib/libqt-mt.so.3
#35 0xb68af1b1 in QEventLoop::enterLoop () from /usr/qt/3/lib/libqt-mt.so.3
#36 0xb68af036 in QEventLoop::exec () from /usr/qt/3/lib/libqt-mt.so.3
#37 0xb689810f in QApplication::exec () from /usr/qt/3/lib/libqt-mt.so.3
#38 0x080595e5 in ?? ()
#39 0xbffee244 in ?? ()
#40 0xbffee244 in ?? ()
#41 0xb61e43f0 in ?? ()
#42 0x00000002 in ?? ()
#43 0xb7fbdfbc in ?? () from /lib/ld-linux.so.2
#44 0xb7fbe870 in ?? ()
#45 0x08061b88 in _IO_stdin_used ()
#46 0xbffee320 in ?? ()
#47 0x08099c48 in ?? ()
#48 0x00000000 in ?? ()