Version:           1.8.2 (using KDE 3.4.2, compiled sources)
Compiler:          gcc version 3.3.4
OS:                Linux (i686) release 2.6.12.4

I used konstruct to fetch the required libraries along with KDE package. The bug happens only when sending mail, and if the user didn't flag 'Store SMTP password'. When user receives mail the 'Cancel' works normally. Does ont depend on whether I'm using Kontact or directly Kmail.

Here's a fresh backtrace from the wizard:

Using host libthread_db library "/lib/libthread_db.so.1".
[Thread debugging using libthread_db enabled]
[New Thread 16384 (LWP 6479)]
[KCrash handler]
#4  0x402cef35 in KMMsgBase::setTransferInProgress ()
   from /opt/kde/lib/libkmailprivate.so
#5  0x40297a31 in KMSender::doSendMsgAux ()
   from /opt/kde/lib/libkmailprivate.so
#6  0x40297821 in KMSender::sendProcStarted ()
   from /opt/kde/lib/libkmailprivate.so
#7  0x4029be50 in KMSender::qt_invoke () from /opt/kde/lib/libkmailprivate.so
#8  0x41d3c77c in QObject::activate_signal ()
   from /usr/local/lib/qt-x11-free-3.3.4/lib/libqt-mt.so.3
#9  0x41d3cdb0 in QObject::activate_signal_bool ()
   from /usr/local/lib/qt-x11-free-3.3.4/lib/libqt-mt.so.3
#10 0x4029c0cb in KMSendProc::started () from /opt/kde/lib/libkmailprivate.so
#11 0x402993b8 in KMSendProc::start () from /opt/kde/lib/libkmailprivate.so
#12 0x00000001 in ?? ()
#13 0xbfe512a8 in ?? ()
#14 0x4054a7f4 in __JCR_LIST__ () from /opt/kde/lib/libkmailprivate.so
#15 0x081e5f10 in ?? ()
#16 0x4054a7f4 in __JCR_LIST__ () from /opt/kde/lib/libkmailprivate.so
#17 0xbfe51458 in ?? ()
#18 0x40296948 in KMSender::doSendMsg () from /opt/kde/lib/libkmailprivate.so

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To reproduce, try to send the mail using an account without stored SMTP password and in the created window click 'Cancel'

Expected behavior: something more interesting :)