MIDI channel assignments lost in parts after save / reopen

I discovered some weird behavior of midi output files generated from parts (not main score):

When playback channels are changed via staff text - say from arco to pizzicato - this is not reflected correctly in the midi output files of parts after close / reopen of the file

Steps to reproduce (you might want to start directly with 4 to produce error):
1) Choose one staff with violin, type some notes and change from arco to pizz or tremolo like in the attached file
2) Create part
3) export parts as midi and inspect file with suited editor (e.g. DAW)
Result achieved & expected: arco notes play on channel 1, pizzicato notes play on 2, tremolo notes on 3
4) Close and reopen file above or use attached one
5) export parts again as midi and inspect with midi editor
Result achieved: all notes are playing on channel 1
Result expected: arco notes play on channel 1, pizzicato notes play on 2, tremolo notes on 3

Some side notes:
- Exporting the main score always gives correct channel assignments
- playback of part in Musescore is correct, as well as playback in main score
- when part is deleted and recreated, part midi is correct again until file is closed / reopened

This behavior is present in v3.0.4 as well as in the nightlies from March 7th and 6th.

I marked it S2-critical as it is blocking my workflow which relies on generating midi from parts to feed (multiple) VSTs in a DAW.