Version:           3.5.1 (using KDE 3.5.1, Kubuntu Package 4:3.5.1-0ubuntu5 dapper)
Compiler:          Target: i486-linux-gnu
OS:                Linux (i686) release 2.6.15-15-686

I hardly suspect it has to do with viewing a video with the embedded kaffeine player. At least I can say that using the embedded player raises unstability in konqueror.

Backtrace follows:

Using host libthread_db library "/lib/tls/i686/cmov/libthread_db.so.1".
[Thread debugging using libthread_db enabled]
[New Thread 915973824 (LWP 3850)]
[KCrash handler]
#6  0x369bae84 in pthread_mutex_lock ()
   from /lib/tls/i686/cmov/libpthread.so.0
#7  0x37e2174e in pthread_mutex_lock () from /lib/tls/i686/cmov/libc.so.6
#8  0x36f57a3c in XUnlockDisplay () from /usr/lib/libX11.so.6
#9  0x36f72ee4 in XrmEnumerateDatabase () from /usr/lib/libX11.so.6
#10 0x36f56ec9 in XKeysymToString () from /usr/lib/libX11.so.6
#11 0x3794fd89 in KKeyServer::Sym::toString (this=0x3f8de6e8, 
    bUserSpace=false) at kkeyserver_x11.cpp:526
#12 0x37950313 in KKeyServer::Sym::toStringInternal (this=0x0)
    at kkeyserver_x11.cpp:532
#13 0x379503b7 in KKey::toStringInternal (this=0x8515304) at kshortcut.cpp:188
#14 0x3795102b in KKeySequence::toStringInternal (this=0x8515300)
    at kshortcut.cpp:380
#15 0x3795288e in KShortcut::toStringInternal (this=0x85152d4, 
    pcutDefault=0x0) at kshortcut.cpp:656
#16 0x37952bab in KAccelBase::insertConnection (this=0x8432b10, 
    pAction=0x85152c8) at kaccelbase.cpp:461
#17 0x3795de13 in KAccelBase::insert (this=0x8432b10, sAction=@0x0, 
    sDesc=@0x0, sHelp=@0x0, rgCutDefaults3=@0x0, rgCutDefaults4=@0x0, 
    pObjSlot=0x0, psMethodSlot=0x0, bConfigurable=true, bEnabled=true)
    at kaccelbase.cpp:142
#18 0x3795e19f in KAccel::insert (this=0x0, sAction=@0x0, sLabel=@0x0, 
    sWhatsThis=@0x0, cutDef=@0x369bae60, pObjSlot=0x0, psMethodSlot=0x0, 
    bConfigurable=true, bEnabled=true) at kaccel.cpp:453
#19 0x36e1ec10 in KAction::updateKAccelShortcut (this=0x98a8110, 
    kaccel=0x8f6d818) at kaction.cpp:456
#20 0x36e1ef7c in KAction::insertKAccel (this=0x98a8110, kaccel=0x8f6d818)
    at kaction.cpp:469
#21 0x36e1f0d1 in KAction::plugShortcut (this=0x98a8110) at kaction.cpp:400
#22 0x36e1f117 in KAction::plug (this=0x98a8110, w=0x8315668, index=9)
    at kaction.cpp:640
#23 0x36d6755b in KXMLGUI::BuildHelper::processActionElement (
    this=0x3f8debd4, e=@0x0, idx=0) at kxmlguifactory_p.cpp:615
#24 0x36dfcfbd in KXMLGUI::BuildHelper::processActionOrCustomElement (
    this=0x3f8debd4, e=@0x3f8deb54, isActionTag=true)
    at kxmlguifactory_p.cpp:595
#25 0x36e819c5 in KXMLGUI::BuildHelper::processElement (this=0x3f8debd4, 
    e=@0x3f8deb54) at kxmlguifactory_p.cpp:572
#26 0x36e81c51 in KXMLGUI::BuildHelper::build (this=0x3f8debd4, element=@0x0)
    at kxmlguifactory_p.cpp:552
#27 0x36e814bc in KXMLGUI::BuildHelper::processContainerElement (
    this=0x3f8ded14, e=@0x3f8dec94, tag=@0x3f8dec64, name=@0x3f8dec60)
    at kxmlguifactory_p.cpp:783
#28 0x36e81b74 in KXMLGUI::BuildHelper::processElement (this=0x3f8ded14, 
    e=@0x3f8dec94) at kxmlguifactory_p.cpp:574
#29 0x36e81c51 in KXMLGUI::BuildHelper::build (this=0x3f8ded14, element=@0x0)
    at kxmlguifactory_p.cpp:552
#30 0x36e814bc in KXMLGUI::BuildHelper::processContainerElement (
    this=0x3f8dee8c, e=@0x3f8dedd4, tag=@0x3f8deda4, name=@0x3f8deda0)
    at kxmlguifactory_p.cpp:783
#31 0x36e81b74 in KXMLGUI::BuildHelper::processElement (this=0x3f8dee8c, 
    e=@0x3f8dedd4) at kxmlguifactory_p.cpp:574
#32 0x36e81c51 in KXMLGUI::BuildHelper::build (this=0x3f8dee8c, element=@0x0)
    at kxmlguifactory_p.cpp:552
#33 0x36e8202c in KXMLGUIFactory::addClient (this=0x82cc1f8, client=0x989f65c)
    at kxmlguifactory.cpp:289
#34 0x36e82606 in KXMLGUIFactory::addClient (this=0x82cc1f8, client=0x97f92b4)
    at kxmlguifactory.cpp:315
#35 0x37faa8eb in KParts::MainWindow::createGUI (this=0x817f380, 
    part=0x97f8fa0) at mainwindow.cpp:131
#36 0x3680c533 in KonqMainWindow::slotPartActivated ()
   from /usr/lib/libkdeinit_konqueror.so
#37 0x3680d0c3 in KonqViewManager::emitActivePartChanged ()
   from /usr/lib/libkdeinit_konqueror.so
#38 0x3683636f in KonqViewManager::qt_invoke ()
   from /usr/lib/libkdeinit_konqueror.so
#39 0x3731c26d in QObject::activate_signal () from /usr/lib/libqt-mt.so.3
#40 0x376ab31e in QSignal::signal () from /usr/lib/libqt-mt.so.3
#41 0x373399cc in QSignal::activate () from /usr/lib/libqt-mt.so.3
#42 0x373414bc in QSingleShotTimer::event () from /usr/lib/libqt-mt.so.3
#43 0x372b265a in QApplication::internalNotify () from /usr/lib/libqt-mt.so.3
#44 0x372b284c in QApplication::notify () from /usr/lib/libqt-mt.so.3
#45 0x37979c7d in KApplication::notify (this=0x3f8df94c, receiver=0x82ebd48, 
    event=0x3f8df5e8) at kapplication.cpp:550
#46 0x37243967 in QApplication::sendEvent () from /usr/lib/libqt-mt.so.3
#47 0x372a4047 in QEventLoop::activateTimers () from /usr/lib/libqt-mt.so.3
#48 0x37257753 in QEventLoop::processEvents () from /usr/lib/libqt-mt.so.3
#49 0x372cb153 in QEventLoop::enterLoop () from /usr/lib/libqt-mt.so.3
#50 0x372cb076 in QEventLoop::exec () from /usr/lib/libqt-mt.so.3
#51 0x372b1169 in QApplication::exec () from /usr/lib/libqt-mt.so.3
#52 0x36834881 in kdemain () from /usr/lib/libkdeinit_konqueror.so
#53 0x37fbe4f4 in kdeinitmain () from /usr/lib/kde3/konqueror.so
#54 0x0804e00f in launch (argc=3, _name=0x81213d4 "konqueror", 
    args=0x812141f "", cwd=0x0, envc=0, envs=0x8121423 "", reset_env=false, 
    tty=0x0, avoid_loops=false, startup_id_str=0x0) at kinit.cpp:637
#55 0x0804e6b3 in handle_launcher_request (sock=8) at kinit.cpp:1203
#56 0x0804ec3d in handle_requests (waitForPid=0) at kinit.cpp:1404
#57 0x0804fd03 in main (argc=2, argv=0x3f8e0484, envp=0x0) at kinit.cpp:1848
#58 0x37d5fea2 in __libc_start_main () from /lib/tls/i686/cmov/libc.so.6
#59 0x0804b7e1 in _start () at ../sysdeps/i386/elf/start.S:119