Key signatures may become out of sync with changes to transposing instruments at multimeasure rests

Issue type

Engraving bug (incorrect score rendering)

Description with steps to reproduce

Key signatures fail to change correctly when adding or deleting a key signature before an instrument change to a transposing instrument at a multimeasure rest.

It seems that the presence of an MMRest when the preceding key signature is changed causes the incorrect key signature to stick; relayout or replacing the MMRest for notes does not cause it to correct itself.

Supporting files, videos and screenshots

The screen recording shows desync with a part layout, but the issue present also in the main score if MMRests are shown.

https://github.com/user-attachments/assets/a49dd088-e7fa-4250-8f7d-3df878e616b4

In which versions of MuseScore Studio is this issue present?

Nightly main

Regression

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

Operating system

Ubuntu 24.04.4 LTS

Additional context

See also #33823.

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