Weird graphics glitch

So I have just installed Mate, for interest sake…and come across a weird glitch. On the desktop, when I right click and get the menu up to change background, etc, the Paste option is greyed out, as it should be with nothing to paste, but it is pulsing/flashing rapidly. Anybody else got this? I tried multiple themes, and it’s consistent.

Maybe some setting for window effects?

Good idea, but doing it even with compositing off. Not a real problem, just a “what the?”.