Crashes when trying to re-enable OpenGL detection. 

Reproducible: Always

Steps to Reproduce:
1. Configure Desktop
2. Desktop Effects
3.Re-enable OpenGL detection.
Actual Results:  
"System Settings closed unexpectedly"

Expected Results:  
Enabled Desktop effects.

-- Backtrace:
Application: System Settings (systemsettings), signal: Segmentation fault
[KCrash Handler]
#6  0x00007ff3e9509397 in nv50_screen_fence_update (pscreen=0xae47b0) at nv50_screen.c:269
#7  0x00007ff3e9549323 in nouveau_fence_update (screen=0xae47b0, flushed=1 '\001') at nouveau_fence.c:141
#8  0x00007ff3e950b21b in nv50_default_flush_notify (chan=<optimized out>) at nv50_context.c:68
#9  0x00007ff3e90ff82c in nouveau_pushbuf_flush (chan=0x966cb0, min=0) at nouveau_pushbuf.c:276
#10 0x00007ff3e90ffb32 in FIRE_RING (chan=0x966cb0) at nouveau_pushbuf.h:101
#11 nouveau_grobj_free (grobj=<optimized out>) at nouveau_grobj.c:102
#12 0x00007ff3e950956e in nv50_screen_destroy (pscreen=0xae47b0) at nv50_screen.c:235
#13 0x00007ff3e94ca010 in dri_destroy_screen_helper (screen=0xa9f240) at dri_screen.c:352
#14 0x00007ff3e94ca0a0 in dri_destroy_screen (sPriv=0x9907b0) at dri_screen.c:362
#15 0x00007ff3e94c6270 in driDestroyScreen (psp=0x9907b0) at ../common/dri_util.c:732
#16 0x00007ff3eb28bd4b in dri2_terminate (drv=<optimized out>, disp=0xad2400) at egl_dri2.c:582
#17 0x00007ff3eb28484d in eglTerminate (dpy=0xad2400) at eglapi.c:351
#18 0x00007ff3eb729cb6 in ?? () from /usr/lib64/kde4/kcm_kwincompositing.so
#19 0x00007ff3eb729f64 in ?? () from /usr/lib64/kde4/kcm_kwincompositing.so
#20 0x00007ff3eb71e6ac in ?? () from /usr/lib64/kde4/kcm_kwincompositing.so
#21 0x00007ff3eb720e97 in ?? () from /usr/lib64/kde4/kcm_kwincompositing.so
#22 0x00007ff3eb71dd61 in ?? () from /usr/lib64/kde4/kcm_kwincompositing.so
#23 0x00007ff3fc7000f1 in QMetaObject::activate (sender=0x96da00, m=<optimized out>, local_signal_index=<optimized out>, argv=0x7fffa0cf3280) at kernel/qobject.cpp:3556
#24 0x00007ff3fda09992 in QAbstractButton::clicked (this=<optimized out>, _t1=false) at .moc/release-shared/moc_qabstractbutton.cpp:220
#25 0x00007ff3fd74860e in QAbstractButtonPrivate::emitClicked (this=<optimized out>) at widgets/qabstractbutton.cpp:548
#26 0x00007ff3fd74994b in QAbstractButtonPrivate::click (this=0x96e030) at widgets/qabstractbutton.cpp:541
#27 0x00007ff3fd749bbc in QAbstractButton::mouseReleaseEvent (this=0x96da00, e=0x7fffa0cf3b50) at widgets/qabstractbutton.cpp:1123
#28 0x00007ff3fd3cf7e4 in QWidget::event (this=0x96da00, event=0x7fffa0cf3b50) at kernel/qwidget.cpp:8362
#29 0x00007ff3fd37f0d4 in notify_helper (e=0x7fffa0cf3b50, receiver=0x96da00, this=0x660430) at kernel/qapplication.cpp:4554
#30 QApplicationPrivate::notify_helper (this=0x660430, receiver=0x96da00, e=0x7fffa0cf3b50) at kernel/qapplication.cpp:4526
#31 0x00007ff3fd384823 in QApplication::notify (this=<optimized out>, receiver=0x96da00, e=0x7fffa0cf3b50) at kernel/qapplication.cpp:4097
#32 0x00007ff3fe0c38f6 in KApplication::notify(QObject*, QEvent*) () from /usr/lib64/libkdeui.so.5
#33 0x00007ff3fc6ec22c in QCoreApplication::notifyInternal (this=0x7fffa0cf4850, receiver=0x96da00, event=0x7fffa0cf3b50) at kernel/qcoreapplication.cpp:876
#34 0x00007ff3fd3800a2 in sendEvent (event=<optimized out>, receiver=<optimized out>) at ../../src/corelib/kernel/qcoreapplication.h:231
#35 QApplicationPrivate::sendMouseEvent (receiver=0x96da00, event=0x7fffa0cf3b50, alienWidget=0x96da00, nativeWidget=0x794520, buttonDown=0x96da00, lastMouseReceiver=..., spontaneous=true) at kernel/qapplication.cpp:3165
#36 0x00007ff3fd3fbe85 in QETWidget::translateMouseEvent (this=0x794520, event=<optimized out>) at kernel/qapplication_x11.cpp:4513
#37 0x00007ff3fd3fad4a in QApplication::x11ProcessEvent (this=0x7fffa0cf4850, event=0x7fffa0cf4410) at kernel/qapplication_x11.cpp:3636
#38 0x00007ff3fd422ae2 in x11EventSourceDispatch (s=0x657f50, callback=0, user_data=0x0) at kernel/qguieventdispatcher_glib.cpp:146
#39 0x00007ff3f966158d in g_main_context_dispatch () from /usr/lib64/libglib-2.0.so.0
#40 0x00007ff3f9661d88 in ?? () from /usr/lib64/libglib-2.0.so.0
#41 0x00007ff3f9661f59 in g_main_context_iteration () from /usr/lib64/libglib-2.0.so.0
#42 0x00007ff3fc71b27f in QEventDispatcherGlib::processEvents (this=0x61e110, flags=<optimized out>) at kernel/qeventdispatcher_glib.cpp:424
#43 0x00007ff3fd42276e in QGuiEventDispatcherGlib::processEvents (this=<optimized out>, flags=<optimized out>) at kernel/qguieventdispatcher_glib.cpp:204
#44 0x00007ff3fc6eb012 in QEventLoop::processEvents (this=<optimized out>, flags=...) at kernel/qeventloop.cpp:149
#45 0x00007ff3fc6eb267 in QEventLoop::exec (this=0x7fffa0cf47e0, flags=...) at kernel/qeventloop.cpp:204
#46 0x00007ff3fc6efdc5 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:1148
#47 0x000000000040b235 in ?? ()
#48 0x00007ff3fbef323d in __libc_start_main () from /lib64/libc.so.6
#49 0x000000000040b289 in _start ()

---------------------
AMD Phenom II x4 945 cpu
nVIDIA GeForce 8500 GT
nouveau Gallium: 0.4 on NV86
OpenGL/ES version: 2.1 Mesa 7.11