@bean
Ah, ok, so you implemented the separate player task finally... nice
I didnt discover it for the latest version, as I seldom use TuneNet menu once I started playback. I only saw it with the older version (dont remember which one).
Well, I think its not really about ReAction and MUI, its about locking the whole screen, resp. missing "sprites" for display dragging actions. ReAction gadgets lock the screen if they update their contents and MUI needs a previously unlocked screen to display the dragging action. So it breaks the dragging action in case the screen is locked at any time the dragging action takes place. Do I see this right?
I had a similar issue with Workbench dragging, I solved this by checking the screen if its locked and if its locked, I stepped over GUI update until the screen is unlocked again. Its not perfect (race conditions still possible), but quite ok.
I think we have to wait for a solution that permits drawing in the background resp. layer-dependend drawing, so that a program doesnt need to lock the whole screen for actions that take place in a specific layer only...
Edit: Another idea traveled through my brain as I read my text again... what about implementing dragging with a "moving layer"? This way layers.library would be able to reconstruct a layer needed by a gadget in a temporary way, until the moving "dragging object" is out of layer range... its really a pity that sprites where dropped back then