Thank you Andrew for reporting steps to reproduce and Andrea (for confirming) AND the dumps.

Try to load any video with audio, then hit play in main window, and while video
is playing - try to drag Brightness/Contrast plugin over whole track. Freeze!

Hm, I definitely have video output set to X11 (not OpenGL-X11).
Just freezed it again, this time by deleting YUV plugin from track while playing.

A fix has been checked into the GIT repository. More rework of the infinite problem of locking issues when multiple operations are queued up. I have added this problem as part of MantisBT #135 so they are related. gg/Phyllis