Newly added part not muted in already generated part scores

[TheStormcrafter]

Issue type

General playback bug

Description with steps to reproduce

In the score I am currently working on, I wanted to export all the part scores as mp3s.
All part scores contained one of the parts.
This was because that part had been unmuted in all part scores.
Upon further investigation, it turned out that adding a new part would leave that part unmuted in all already generated part scores.
This seems to be an issue of the files, I confirmed on the MuseScore Discord that someone else also experiences this issue using the file I provided.
Another unrelated score of mine also experience this issue.
An older score (pre 4.4.) did not experience this issue, though I don´t want to fix the issue on that version.

Supporting files, videos and screenshots

ENSPK-2024-09-29-2-GonnaFlyNow.zip

What is the latest version of MuseScore Studio where this issue is present?

4.4.2

Regression

Yes, this used to work in a previous version of MuseScore 4.x

Operating system

Win11

Additional context

Marc Sabatella stated, he could reproduce this in a new score by generating a part score, modifying it and than adding a new part.

Checklist

• This report follows the guidelines for reporting bugs and issues
• I have verified that this issue has not been logged before, by searching the issue tracker for similar issues
• I have attached all requested files and information to this report
• I have attempted to identify the root problem as concisely as possible, and have used minimal reproducible examples where possible

[MarcSabatella]

From a little experimentation I did, the trigger seems be the following:

1. the score must have parts already generated
2. one or more of those parts must contain an instrument with have instrument changes within them
3. a new instrument must be added to the score

Under these conditions, any of the parts that contain instruments with instrument changes will have the newly added instrumented not muted. So playing or exporting that part will also include the music from the new instrument, even though it is hidden.

[zacjansheski]

Regression occured between 4.3.2 and 4.4.0