Adding three effects to a clip on time line, then enabling & disabling them
and playing with options:

#0  0xb7688115 in QDomNodePrivate::ownerDocument (this=0xa9a020a)
    at dom/qdom.cpp:1863
#1  0xb7694788 in QDomNodeListPrivate::item (this=0xa9ac310, index=0)
    at dom/qdom.cpp:1257
#2  0xb76947f2 in QDomNodeList::item (this=0xbfc3d28c, index=0)
    at dom/qdom.cpp:1393
#3  0x081683fa in EffectsList::effectNames (this=0x9ddb240)
    at /home/mcfrisk/src/kdenlive-svn/src/effectslist.cpp:113
#4  0x08153be8 in ClipItem::setEffectAt (this=0x9ddb190, ix=3, effect=
        {<QDomNode> = {impl = 0xbfc3d4b4}, <No data fields>})
    at /home/mcfrisk/src/kdenlive-svn/src/clipitem.cpp:1282
#5  0x0813767e in CustomTrackView::updateEffect (this=0xa422e58, track=4, pos=
      {m_time = -0.15495309222721287, static s_delta = 1.0000000000000001e-05}, effect={<QDomNode> = {impl = 0xbfc3d580}, <No data fields>}, ix=3,
    triggeredByUser=true)
    at /home/mcfrisk/src/kdenlive-svn/src/customtrackview.cpp:1401
#6  0x0817d4f6 in EditEffectCommand::redo (this=0xaba4e20)
    at /home/mcfrisk/src/kdenlive-svn/src/editeffectcommand.cpp:69
#7  0xb6f47d58 in QUndoStack::push (this=0xa411bf8, cmd=0xaba4e20)
    at util/qundostack.cpp:543
#8  0x0810b2c3 in CustomTrackView::slotUpdateClipEffect (this=0xa422e58,
    clip=0x9ddb190, oldeffect=
        {<QDomNode> = {impl = 0xbfc3d71c}, <No data fields>}, effect=
        {<QDomNode> = {impl = 0xbfc3d718}, <No data fields>}, ix=3)
    at /home/mcfrisk/src/kdenlive-svn/src/customtrackview.cpp:1455
#9  0x0812d43d in CustomTrackView::qt_metacall (this=0xa422e58, 
    _c=QMetaObject::InvokeMetaMethod, _id=22, _a=0xbfc3d804)
    at /home/mcfrisk/src/kdenlive-svn/build/src/cmake_bindir/customtrackview.moc:198
#10 0xb72fcb98 in QMetaObject::activate (sender=0xa1100f0, 
    from_signal_index=29, to_signal_index=29, argv=0xbfc3d804)
    at kernel/qobject.cpp:3120
#11 0xb72fd822 in QMetaObject::activate (sender=0xa1100f0, m=0x82b5994, 
    local_signal_index=2, argv=0xbfc3d804) at kernel/qobject.cpp:3194
#12 0x0817dd87 in EffectStackView::updateClipEffect (this=0xa1100f0, 
    _t1=0x9ddb190, _t2={<QDomNode> = {impl = 0xbfc3d848}, <No data fields>}, 
    _t3={<QDomNode> = {impl = 0xbfc3d844}, <No data fields>}, _t4=3)
    at /home/mcfrisk/src/kdenlive-svn/build/src/cmake_bindir/effectstackview.moc:138
#13 0x0817e019 in EffectStackView::slotUpdateEffectParams (this=0xa1100f0, 
    old=@0xbfc3db94, e=@0xa115b68)
    at /home/mcfrisk/src/kdenlive-svn/src/effectstackview.cpp:127
#14 0x08180309 in EffectStackView::qt_metacall (this=0xa1100f0, 
    _c=QMetaObject::InvokeMetaMethod, _id=8, _a=0xbfc3d95c)
    at /home/mcfrisk/src/kdenlive-svn/build/src/cmake_bindir/effectstackview.moc:105
#15 0xb72fcb98 in QMetaObject::activate (sender=0xa115b48, 
    from_signal_index=27, to_signal_index=27, argv=0xbfc3d95c)
    at kernel/qobject.cpp:3120
#16 0xb72fd822 in QMetaObject::activate (sender=0xa115b48, m=0x8294e68, 
    local_signal_index=0, argv=0xbfc3d95c) at kernel/qobject.cpp:3194
#17 0x08077aab in EffectStackEdit::parameterChanged (this=0xa115b48, 
    _t1=@0xbfc3db94, _t2=@0xa115b68)
    at /home/mcfrisk/src/kdenlive-svn/build/src/cmake_bindir/moc_effectstackedit.cpp:95
#18 0x08185a64 in EffectStackEdit::collectAllParameters (this=0xa115b48)
    at /home/mcfrisk/src/kdenlive-svn/src/effectstackedit.cpp:496
#19 0x08078c2b in EffectStackEdit::qt_metacall (this=0xa115b48, 
    _c=QMetaObject::InvokeMetaMethod, _id=4, _a=0xbfc3dc9c)
    at /home/mcfrisk/src/kdenlive-svn/build/src/cmake_bindir/moc_effectstackedit.cpp:82
#20 0xb72fcb98 in QMetaObject::activate (sender=0xac9b408, 
    from_signal_index=27, to_signal_index=27, argv=0xbfc3dc9c)
    at kernel/qobject.cpp:3120
#21 0xb72fd822 in QMetaObject::activate (sender=0xac9b408, m=0xb7138ad4, 
    local_signal_index=0, argv=0xbfc3dc9c) at kernel/qobject.cpp:3194
#22 0xb6f51243 in QAbstractSlider::valueChanged (this=0xac9b408, _t1=331)
    at .moc/release-shared/moc_qabstractslider.cpp:176
#23 0xb6c7c959 in QAbstractSlider::setValue (this=0xac9b408, value=331)
    at widgets/qabstractslider.cpp:531
#24 0xb6c7ca21 in QAbstractSlider::triggerAction (this=0xac9b408, 
    action=QAbstractSlider::SliderMove) at widgets/qabstractslider.cpp:620
#25 0xb6c7cf00 in QAbstractSlider::setSliderPosition (this=0xac9b408, 
    position=331) at widgets/qabstractslider.cpp:488
#26 0xb6d2b871 in QSlider::mouseMoveEvent (this=0xac9b408, ev=0xbfc3e3bc)
    at widgets/qslider.cpp:524
#27 0xb68ef21d in QWidget::event (this=0xac9b408, event=0xbfc3e3bc)
    at kernel/qwidget.cpp:7506
#28 0xb6c7c7c4 in QAbstractSlider::event (this=0xac9b408, e=0xbfc3e3bc)
    at widgets/qabstractslider.cpp:855
#29 0xb6d2be9e in QSlider::event (this=0xac9b408, event=0xbfc3e3bc)
    at widgets/qslider.cpp:436
#30 0xb68987bc in QApplicationPrivate::notify_helper (this=0x9d8b2d8, 
    receiver=0xac9b408, e=0xbfc3e3bc) at kernel/qapplication.cpp:4057
#31 0xb68a1441 in QApplication::notify (this=0xbfc3fc44, receiver=0xac9b408, 
    e=0xbfc3e3bc) at kernel/qapplication.cpp:3759
#32 0xb7ca95ed in KApplication::notify (this=0xbfc3fc44, receiver=0xac9b408, 
    event=0xbfc3e3bc) at ../../kdeui/kernel/kapplication.cpp:307
#33 0xb72e6a2b in QCoreApplication::notifyInternal (this=0xbfc3fc44, 
    receiver=0xac9b408, event=0xbfc3e3bc) at kernel/qcoreapplication.cpp:610
#34 0xb68a04ae in QApplicationPrivate::sendMouseEvent (receiver=0xac9b408, 
    event=0xbfc3e3bc, alienWidget=0xac9b408, nativeWidget=0xa10cb28,
    buttonDown=0xb71459e0, lastMouseReceiver=@0xb71459e4)
    at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:216
#35 0xb690fdc5 in QETWidget::translateMouseEvent (this=0xa10cb28, 
    event=0xbfc3f96c) at kernel/qapplication_x11.cpp:4448
#36 0xb690f266 in QApplication::x11ProcessEvent (this=0xbfc3fc44, 
    event=0xbfc3f96c) at kernel/qapplication_x11.cpp:3444
#37 0xb69399a2 in x11EventSourceDispatch (s=0x9d8e468, callback=0, 
    user_data=0x0) at kernel/qguieventdispatcher_glib.cpp:146
#38 0xb5fe3848 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#39 0xb5fe6d73 in ?? () from /usr/lib/libglib-2.0.so.0
#40 0x09d8cd08 in ?? ()
#41 0x00000000 in ?? ()