I attached a level where you can see the bug.
This would not be a problem with 1 song. The problem comes when you want to use 2 songs or more (like in the level).
I think the problem ocurrs with the None option in the Level Music box
The solution would be adding an option like in the image. That would not stop the song that the level is already playing.
(For example, if in Section 1 you have SMB3 Overworld and in Section 2 "Not Set", when you enter the section 2 via warping, the level will play SMB3 Overworld.)