Used send contact to, then enabled S/MIME signature.
On the attachement pressed right mouse button menu and "Ansehen"
(should be raw view).

Kontact: 1.0 (proko2 branch after 2.1.5), Revision 600703.
Debian Sarge (ppc) with KDE: 3.3.2 Qt: 3.3.4

Using host libthread_db library "/usr/lib/debug/libthread_db.so.1".
[Thread debugging using libthread_db enabled]
[New Thread 16384 (LWP 24572)]
[New Thread 32769 (LWP 24589)]
[KCrash handler]
#4  0x0e2abc40 in kill () from /usr/lib/debug/libc.so.6
#5  0x0e6e98cc in pthread_kill (thread=24572, signo=6) at signals.c:65
#6  0x0e6e9d48 in __pthread_raise (sig=24572) at signals.c:187
#7  0x0e2aba28 in *__GI_raise (sig=671106178)
    at ../linuxthreads/sysdeps/unix/sysv/linux/raise.c:34
#8  0x0e2ad140 in *__GI_abort () at ../sysdeps/generic/abort.c:88
#9  0x0e2a46d4 in *__GI___assert_fail (
    assertion=0xd8e6e30 "mBodyDecodedSize < 0 || (unsigned int)mBodyDecodedSize == result.size()", file=0xd8e6ca4 "kmmsgpart.cpp", line=6, 
    function=0xe3c4d7c "\016;Âp\016/Y´") at assert.c:83
#10 0x0d6ce6ac in KMMessagePart::bodyDecodedBinary ()
   from /local-vol1/bernhard/kde/install-proko2/lib/libkmailprivate.so.0
#11 0x0d6859e4 in KMComposeWin::viewAttach ()
   from /local-vol1/bernhard/kde/install-proko2/lib/libkmailprivate.so.0
#12 0x0d6855f0 in KMComposeWin::slotAttachView ()
   from /local-vol1/bernhard/kde/install-proko2/lib/libkmailprivate.so.0
#13 0x0d671050 in KMComposeWin::qt_invoke ()
   from /local-vol1/bernhard/kde/install-proko2/lib/libkmailprivate.so.0
#14 0x0eb1e4e4 in QObject::activate_signal () from /usr/lib/libqt-mt.so.3
#15 0x0ee62fcc in QSignal::signal () from /usr/lib/libqt-mt.so.3
#16 0x0eb38d18 in QSignal::activate () from /usr/lib/libqt-mt.so.3
#17 0x0ec28008 in QPopupMenu::mouseReleaseEvent () from /usr/lib/libqt-mt.so.3
#18 0x0eb56c08 in QWidget::event () from /usr/lib/libqt-mt.so.3
#19 0x0eabb8e8 in QApplication::internalNotify () from /usr/lib/libqt-mt.so.3
#20 0x0eabb12c in QApplication::notify () from /usr/lib/libqt-mt.so.3
#21 0x0f224068 in KApplication::notify () from /usr/lib/libkdecore.so.4
#22 0x0ea4d600 in QETWidget::translateMouseEvent ()
   from /usr/lib/libqt-mt.so.3
#23 0x0ea4b8b4 in QApplication::x11ProcessEvent () from /usr/lib/libqt-mt.so.3
#24 0x0ea637d8 in QEventLoop::processEvents () from /usr/lib/libqt-mt.so.3
#25 0x0eacf2d0 in QEventLoop::enterLoop () from /usr/lib/libqt-mt.so.3
#26 0x0eacf0dc in QEventLoop::exec () from /usr/lib/libqt-mt.so.3
#27 0x0eabbb7c in QApplication::exec () from /usr/lib/libqt-mt.so.3
#28 0x10010b2c in main ()