Version:            (using KDE KDE 3.5.4)
Installed from:    Gentoo Packages
Compiler:          gcc 4.1.1 CFLAGS="-O2 -ggdb -march=i686 -pipe -fno-omit-frame-pointer -msse -msse2 -msse3" CXXFLAGS="${CFLAGS} -fvisibility-inlines-hidden" LDFLAGS="-Wl,-O1 -Wl,--as-needed -Wl,--hash-style=both"
OS:                Linux

Happened only once so far, hard to reproduce. I hope my backtrace helps.

Backtrace:
----------
Using host libthread_db library "/lib/libthread_db.so.1".
[Thread debugging using libthread_db enabled]
[New Thread -1231055184 (LWP 9338)]
[KCrash handler]
#6  0xb6299105 in TaskContainer::popupMenu (this=0x88be5f8, action=0)
    at taskcontainer.cpp:1120
#7  0xb629dddf in TaskContainer::performAction (this=0x88be5f8, action=0)
    at taskcontainer.cpp:942
#8  0xb62a81d8 in TaskContainer::mousePressEvent (this=0x88be5f8, 
    e=0xbf89430c) at taskcontainer.cpp:876
#9  0xb75891db in QWidget::event (this=0x88be5f8, e=0xbf89430c)
    at kernel/qwidget.cpp:4696
#10 0xb74f10e7 in QApplication::internalNotify (this=0x8070cb8, 
    receiver=0x88be5f8, e=0xbf89430c) at kernel/qapplication.cpp:2635
#11 0xb74f2118 in QApplication::notify (this=0x8070cb8, receiver=0x88be5f8, 
    e=0xbf89430c) at kernel/qapplication.cpp:2421
#12 0xb7b47a8e in KApplication::notify (this=0x8070cb8, receiver=0x88be5f8, 
    event=0xbf89430c) at kapplication.cpp:550
#13 0xb7492802 in QETWidget::translateMouseEvent (this=0x88be5f8, 
    event=0xbf8946a8) at kernel/qapplication.h:523
#14 0xb749196f in QApplication::x11ProcessEvent (this=0x8070cb8, 
    event=0xbf8946a8) at kernel/qapplication_x11.cpp:3564
#15 0xb74a1cf1 in QEventLoop::processEvents (this=0x8099240, 
    flags=<value optimized out>) at kernel/qeventloop_x11.cpp:192
#16 0xb7507e91 in QEventLoop::enterLoop (this=0x8099240)
    at kernel/qeventloop.cpp:198
#17 0xb7507d16 in QEventLoop::exec (this=0x8099240)
    at kernel/qeventloop.cpp:145
#18 0xb74f0c9f in QApplication::exec (this=0x8070cb8)
    at kernel/qapplication.cpp:2758
#19 0xb68d21db in kdemain (argc=1, argv=0x80789a8) at main.cpp:146
#20 0xb72b5594 in kdeinitmain (argc=1, argv=0x80789a8) at kicker_dummy.cpp:3
#21 0x0804e6a7 in launch (argc=1, _name=0x8078f2c "kicker", 
    args=0x8078f33 "", cwd=0x0, envc=0, envs=0x8078f37 "", reset_env=false, 
    tty=0x0, avoid_loops=false, startup_id_str=0x8050747 "0") at kinit.cpp:639
#22 0x0804ef49 in handle_launcher_request (sock=8) at kinit.cpp:1206
#23 0x0804f2cc in handle_requests (waitForPid=0) at kinit.cpp:1407
#24 0x0804fc88 in main (argc=3, argv=0xbf894f94, envp=0xbf894fa4)
    at kinit.cpp:1863