I have NOT tried update GUI.. I will try that, thanks!
For the music room, I noticed that you have the list in different orders in the code in a few places...
I noticed that by default, the next/prev was using the order you have in the definitions.rpy music init section, which is reversed compared to the buttons on the music room screen and is ALSO the alphabetical order of the filenames which is the (reversed) order they play in.
I don't think it's a Ren'Py bug.
This is why I thought that just renaming the audio files would be the easiest fix.