Version:           unknown (using 4.00.81 (KDE 4.0.81 >= 20080527), compiled sources)
Compiler:          gcc
OS:                Linux (i686) release 2.6.24-16-generic

As per description, I used the kcm accessible via right click to enable and disable....
Effects seemed to have enabled correctly, because I could see the 'accept this configuration?' dialog, and when I pressed ok I had woobly windows. :-)
I turned back to no-effects some seconds (10?) later, and bang!

bt:

Application: KWin (kwin), signal SIGABRT
[Thread debugging using libthread_db enabled]
[New Thread 0xb646b720 (LWP 14101)]
[KCrash handler]
#6  0xb7f1d410 in __kernel_vsyscall ()
#7  0xb6712085 in raise () from /lib/tls/i686/cmov/libc.so.6
#8  0xb6713a01 in abort () from /lib/tls/i686/cmov/libc.so.6
#9  0xb670b10e in __assert_fail () from /lib/tls/i686/cmov/libc.so.6
#10 0xb7efc27a in KWin::SceneOpenGL::windowDeleted (this=0x8394950, 
    c=0x8312410)
    at /home/me/kde4/src/kdebase/workspace/kwin/scene_opengl.cpp:782
#11 0xb7eed696 in KWin::Workspace::finishCompositing (this=0x8094d28)
    at /home/me/kde4/src/kdebase/workspace/kwin/composite.cpp:227
#12 0xb7e842fb in KWin::Workspace::slotReconfigure (this=0x8094d28)
    at /home/me/kde4/src/kdebase/workspace/kwin/workspace.cpp:1046
#13 0xb7e84b83 in KWin::Workspace::qt_metacall (this=0x8094d28, 
    _c=QMetaObject::InvokeMetaMethod, _id=111, _a=0xbfe24cf8)
    at /home/me/kde4/src/kdebase/build/workspace/kwin/workspace.moc:407
#14 0xb79aed19 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#15 0xb79af3e2 in QMetaObject::activate () from /usr/lib/libQtCore.so.4
#16 0xb79ec627 in QTimer::timeout () from /usr/lib/libQtCore.so.4
#17 0xb79b5e9e in QTimer::timerEvent () from /usr/lib/libQtCore.so.4
#18 0xb79aa4ba in QObject::event () from /usr/lib/libQtCore.so.4
#19 0xb6ea3cfc in QApplicationPrivate::notify_helper ()
   from /usr/lib/libQtGui.so.4
#20 0xb6ea8889 in QApplication::notify () from /usr/lib/libQtGui.so.4
#21 0xb6b9394b in KApplication::notify (this=0xbfe25450, receiver=0x8094e8c, 
    event=0xbfe251e8)
    at /home/me/kde4/src/kdelibs/kdeui/kernel/kapplication.cpp:311
#22 0xb7ea2838 in KWin::Application::notify (this=0xbfe25450, o=0x8094e8c, 
    e=0xbfe251e8) at /home/me/kde4/src/kdebase/workspace/kwin/main.cpp:368
#23 0xb7999ed9 in QCoreApplication::notifyInternal ()
   from /usr/lib/libQtCore.so.4
#24 0xb79c79c1 in ?? () from /usr/lib/libQtCore.so.4
#25 0xb79c5260 in ?? () from /usr/lib/libQtCore.so.4
#26 0xb65a9bf8 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#27 0xb65ace5e in ?? () from /usr/lib/libglib-2.0.so.0
#28 0xb65ad3ac in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#29 0xb79c57d1 in QEventDispatcherGlib::processEvents ()
   from /usr/lib/libQtCore.so.4
#30 0xb6f36fd5 in ?? () from /usr/lib/libQtGui.so.4
#31 0xb799915d in QEventLoop::processEvents () from /usr/lib/libQtCore.so.4
#32 0xb79992ed in QEventLoop::exec () from /usr/lib/libQtCore.so.4
#33 0xb799b56d in QCoreApplication::exec () from /usr/lib/libQtCore.so.4
#34 0xb6ea3657 in QApplication::exec () from /usr/lib/libQtGui.so.4
#35 0xb7ea4204 in kdemain (argc=3, argv=0xbfe25634)
    at /home/me/kde4/src/kdebase/workspace/kwin/main.cpp:510
#36 0x08048766 in main (argc=)
    at /home/me/kde4/src/kdebase/build/workspace/kwin/kwin_dummy.cpp:3
#0  0xb7f1d410 in __kernel_vsyscall ()