This is a shenanigan that some of the songs may engage in that is normally not recoverable without editing some other song to set the MVOL DSP registers as well. This is because the MVOL DSP registers are normally set once, and only once: at the very beginning, and it also affects every single piece of SFX, since it's the main volume being affected.
To partially alleviate this (though again, it won't help all of the SFX-related shenanigans that occur as a side effect), the MVOL DSP registers can be reset to $7F after initializing a song so that it doesn't result in problems for all of the other songs.
This is a shenanigan that some of the songs may engage in that is normally not recoverable without editing some other song to set the MVOL DSP registers as well. This is because the MVOL DSP registers are normally set once, and only once: at the very beginning, and it also affects every single piece of SFX, since it's the main volume being affected.
To partially alleviate this (though again, it won't help all of the SFX-related shenanigans that occur as a side effect), the MVOL DSP registers can be reset to $7F after initializing a song so that it doesn't result in problems for all of the other songs.