I have some additional information on this issue tracker here:
https://bugzilla.rpmfusion.org/show_bug.cgi?id=2553
It appears that if PulseAudio is not installed and AlsaDefault is used, that the GUI will lock up if Play and then Stop is pressed.
If they change the audio device to AlsaHw0 then the problem does not occur.
Any idea what's going on here?
Thanks,
Richard