MusicXML percussion staves get imported using piano sound

I'm assuming this is a relatively recent regression, but perhaps not.

1) new score for drumset
2) add some notes
3) export to MusicXML
4) import
5) play

Result: piano sounds

Oddly, everything looks to be in place for this to work. And it does work if you save/reload the score in MSCZ format. Or if you go to the Mixer and uncheck then re-check the drumset box. So somehow, it seems the playback info is not getting initialized properly, but all else is OK. In that sense I don't think it's related to #57751: Import of MusicXML file with no drum set info should assume reasonable defaults but maybe somehow it is?