Version:           3.0 (using KDE KDE 3.5.1)
Installed from:    Debian testing/unstable Packages
OS:                Linux

Several windows opened, including Crossover setup, firefox windows, kontact, konsole and some kedit windows. One of kedit windows is flagged "keep above others" to act as a logbook.

I've pushed "Show Desktop" twice, then kwin crashed..

That's what i've got:

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(no debugging symbols found)
Using host libthread_db library "/lib/tls/i686/cmov/libthread_db.so.1".
(no debugging symbols found)
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[Thread debugging using libthread_db enabled]
[New Thread -1229072704 (LWP 24355)]
(no debugging symbols found)
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[KCrash handler]
#6  0xb77f6bd7 in NETWinInfo::windowType () from /usr/lib/libkdecore.so.4
#7  0xb7ef0d49 in KWinInternal::Client::windowType ()
   from /usr/lib/libkdeinit_kwin.so
#8  0xb7ef11ac in KWinInternal::Client::isTopMenu ()
   from /usr/lib/libkdeinit_kwin.so
#9  0xb7f1ac79 in KWinInternal::Workspace::updateMinimizedOfTransients ()
   from /usr/lib/libkdeinit_kwin.so
#10 0xb7f1ae35 in KWinInternal::Client::unminimize ()
   from /usr/lib/libkdeinit_kwin.so
#11 0xb7f1be94 in KWinInternal::Workspace::setShowingDesktop ()
   from /usr/lib/libkdeinit_kwin.so
#12 0xb7f1c0e8 in KWinInternal::RootInfo::changeShowingDesktop ()
   from /usr/lib/libkdeinit_kwin.so
#13 0xb781148f in NETRootInfo::event () from /usr/lib/libkdecore.so.4
#14 0xb7811a34 in NETRootInfo::event () from /usr/lib/libkdecore.so.4
#15 0xb7efafa2 in KWinInternal::Workspace::netCheck ()
   from /usr/lib/libkdeinit_kwin.so
#16 0xb7f3303f in KWinInternal::Workspace::workspaceEvent ()
   from /usr/lib/libkdeinit_kwin.so
#17 0xb7f3392e in KWinInternal::Application::x11EventFilter ()
   from /usr/lib/libkdeinit_kwin.so
#18 0xb70a6805 in qt_set_x11_event_filter () from /usr/lib/libqt-mt.so.3
#19 0xb70b37b1 in QApplication::x11ProcessEvent () from /usr/lib/libqt-mt.so.3
#20 0xb70cd8c0 in QEventLoop::processEvents () from /usr/lib/libqt-mt.so.3
#21 0xb7142da2 in QEventLoop::enterLoop () from /usr/lib/libqt-mt.so.3
#22 0xb7142ccb in QEventLoop::exec () from /usr/lib/libqt-mt.so.3
#23 0xb7129225 in QApplication::exec () from /usr/lib/libqt-mt.so.3
#24 0xb7f304af in kdemain () from /usr/lib/libkdeinit_kwin.so
#25 0xb7c85eb0 in __libc_start_main () from /lib/tls/i686/cmov/libc.so.6
#26 0x080483d1 in ?? ()
------------------------------------------------------------

I had to run
CRTL-ALT-F1 for text console 
$ DISPLAY=:0 kwin&
to restore workplace and continue working

tried to reproduce -- the crash is reproduceable!

I have Debian unstable updated from Debian Sarge on my Pentium-M Compaq Evo n620c laptop.