Webcam and XFCE transparency conflict?

I found recently that my webcam seemed to have stopped working - or to be more accurate, would work only intermittently and then only if called from the terminal.

The symptoms:

- called from the simple desktop, the webcam window would open, but the picture area remained grey. Video recording produced a video file, but its contents were entirely black. Picture capture worked.

- Called from the terminal, sometimes the same happened; sometimes the application started correctly. I can't actually see why this should be, as the script (ucview.new) called by the icon simply kills any running instances of ucview before starting a new one. It is, of course, possible that the intermittent nature of the fault meant that by coincidence it was only these times which worked.

Nothing unusual was reported to the terminal (several Gtk-CRITICAL errors, but that's par for the course).

Since I don't use the webcam often, I couldn't tie this in to any other changes, and was starting to assume it was a hardware issue in view of the intermittent nature of the fault. However after trying a different Linux version on Live-USB and finding that there were no issues at all on that system, I looked again.

I have now found that disabling XFCE transparency (xfce-setting-show -> Window Manager Tweaks -> Compositor tab) brings the webcam back to normality. Presumably the problems started after I enabled transparency, and I just didn't realise for a while due to non-use of the camera.

I wonder if this might be an answer to some of the issues other people have reported about the webcam; probably not all of them, but it may help with some.