Hi, I do not know if this is a bug but at least I think it is not correct and should not behave like that, because if you want to change the song playback speed then you use "Set playback rate".
The issue is:
Set Timescale to >1
Play a song, then the song playback speed will be affected by the timescale of the game.
Set timescale to <1
Play a song, then the song playback speed will not be affected by the game timescale.
I think there should be the option (when playing a song) to allow if the song will be affected by timescale.
In the capx press the keys "+" and "-" and listen to the music track, you can also allow yourself to dance while you wait for the single payment for C3!