If while a file is playing one opens the Extended Controls > Image Adjustment and clicks "enable" the video disapears and the audio continues to play.
If, one leaves the "enable" checked and goes to preferences, does a "reset all" and "save" the dialog, one can again restart a video and see the video and hear the audio, however, the adjustments under "image adjustment" are completely innefective, except for the "opaqueness" slider and the "invert colors" check box.
unchecking "enable" for image adjustment, then rechecking it again causes the video to disapear. stopping play and starting the same or a different video with the "enable" box checked yields playing audio only without video, as if you had checked the "enable" box whilst playing.
This has been the case with the OS X nightlies of the last several weeks, and used to function well on this setup.
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Playing on latest OS X Tiger w/ all updates. Dual 800 G4 Quicksilver mac w/ 1.25 GB memory, lots of free space, permissions and file system in good order.