Replacing a stave spacer with another is not undoable

Issue type

UX/Interaction bug (incorrect behaviour)

Description with steps to reproduce

Dragging a stave spacer on top of another of a different type replaces the original spacer correctly, but Undo removes any spacers rather than reinstating the original.

Supporting files, videos and screenshots

https://github.com/user-attachments/assets/377e8a9e-92d1-48c0-8978-ca1d639bffb9

In which versions of MuseScore Studio is this issue present?

Latest main

Regression

No.

Operating system

macOS 26.5.2

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