Comment 6 for bug 1410457

Top frame of LP's backtrace rubbish. I got the following:

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7fb6d7051700 (LWP 3053)]
0x00007fb73bf9c463 in DisplayWindow::makeCurrent() () from /usr/lib/x86_64-linux-gnu/qt5/plugins/platforms/libqpa-mirserver.so
(gdb) bt
#0 0x00007fb73bf9c463 in DisplayWindow::makeCurrent() () from /usr/lib/x86_64-linux-gnu/qt5/plugins/platforms/libqpa-mirserver.so
#1 0x00007fb73bf9ec07 in MirOpenGLContext::makeCurrent(QPlatformSurface*) () from /usr/lib/x86_64-linux-gnu/qt5/plugins/platforms/libqpa-mirserver.so
#2 0x00007fb7456555c2 in QOpenGLContext::makeCurrent (this=0x10a92a0, surface=0xce9960) at kernel/qopenglcontext.cpp:813
#3 0x00007fb744abfb12 in QSGRenderThread::sync (this=0x131bc90) at scenegraph/qsgthreadedrenderloop.cpp:537
#4 0x00007fb744abfe98 in QSGRenderThread::syncAndRender (this=0x131bc90) at scenegraph/qsgthreadedrenderloop.cpp:587
#5 0x00007fb744ac07d8 in QSGRenderThread::run (this=0x131bc90) at scenegraph/qsgthreadedrenderloop.cpp:704
#6 0x00007fb743b3dd2e in QThreadPrivate::start (arg=0x131bc90) at thread/qthread_unix.cpp:345
#7 0x00007fb7423690a5 in start_thread (arg=0x7fb6d7051700) at pthread_create.c:309
#8 0x00007fb7432b190d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111

and the unity8 log shows me:

QtCompositor::setAllWindowsExposed false
DisplayWindow::event got QEvent::Hide
QtCompositor::setAllWindowsExposed true
DisplayWindow::event got QEvent::Show

So appears as if Qt is trying to render with the display off - which will crash.