Thanks, but resetting the tray cache was no help, unfortunatly. Just relogging hides all but the standard Speaker & Action Center icons.
I have been looking into the registry, and of course have been changing paths (otherwise nothing would work anymore, no?), but in this case, I am pretty clueless what to search for.
got 2 nodes "PromotedIcon" 1 & 2, but no content or something that would indicate anything at all.