Conversion mscz to musicxml: Percussion sounds get lost

Hi everyone,

I created a mscz file with piano and percussion in the current Version of MuseScore (3.1.0.7078). The playback sounds work fine.
Next I converted the mscz file to musicxml via Command Line (Windows 10):

Musescore3.exe pt.mscz -o out.musicxml

When I open the musicxml file in Musescore the percussion won't play the correct sound anymore. It seems like the midi channel gets changed or so? The percussion is play with piano sound.

This kind of transformation worked before, but today it had these problems.

The idea is to write a score in Musescore then to programmatically change the musicxml (I use PHP and XPath) and create audio files from the edited musicxml. I create mp3 files with different tempos for example. As I said this worked before. But now even without changing the file it get the wrong sound.

Thank you in advance for your help and greetings from Freiburg i. Brsg.
Martin