Update instrument when changing default instrument

[CubikingChill]

Issue type

UX/Interaction bug (incorrect behaviour)

Description with steps to reproduce

1. Open a score
2. Change the default instrument VIA editstaff dialog, click apply then OK

Now the clef is changed but instrument is not changed. (Not shown in the video tho)

Supporting files, videos and screenshots

2026-04-11.22-46-20.mp4

In which versions of MuseScore Studio is this issue present?

Latest master nightly

Regression

Yes, this works in the latest released version and is broken in the nightly builds

Operating system

Win10

Additional context

Change the default instrument VIA layout doesn't have the bug.
This was working when I was dealing with a similar issue #32630
No such bug on latest 4.7 nightly

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