Deleted title frame in main score reappears when creating parts

Issue type

UX/Interaction bug (incorrect behaviour)

Description with steps to reproduce

1. Delete the title frame at the beginning of the main score
2. Create a part
3. Switch back to the main score
   RESULT: A vertical frame has been added at the top of the main score

Supporting files, videos and screenshots

https://github.com/user-attachments/assets/43385fe8-5d95-4e07-85cc-6c841886538d

In which versions of MuseScore Studio is this issue present?

Nightly main

Regression

No.

Operating system

macOS 26.6.1

Additional context

No response

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

Start by reproducing the reported sequence in MuseScore Studio: delete the title frame in the main score, create a part, and return to the main score. Trace the part-creation flow and score/frame state to determine why the deleted frame returns; done means the frame remains deleted after creating and switching between parts.