This is more a GUI bug than anything else, just something I've noticed in recent releases of AM on Mac. It happens on mixers and it concerns the mute and solo buttons. Normally, when an "m" or "s" button is ON, those letters m and s are surrounded by a white square. But sometimes, and I am not quite sure what sequence of actions makes this happen, a pale gray square appears and remains there for a long while -- until I touch it with the cursor and it goes away. (This is the same gray square that appears when the cursor just touches the m or s without a mouse click.)
I think I may have seen something similar with the preset numbers on contraptions, a sort of lingering highlight.
No big deal, just something I've noticed.