Explode always explodes entire bar

Issue type

UX/Interaction bug (incorrect behaviour)

Description with steps to reproduce

1. Select a chord on the last beat in a bar
2. Explode

Expected: the last beat in this staff and the ones below it are affected.

Actually: the whole bar is affected, as if I had selected the whole bar first.

Supporting files, videos and screenshots

In which versions of MuseScore Studio is this issue present?

OS: macOS Sequoia (15.7.7), Arch.: arm64, MuseScore Studio version (64-bit): 4.7.4-260706075, revision: github-musescore-musescore-7688c00

Regression

I was unable to check

Operating system

macOS

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

Reproduce the issue in MuseScore Studio 4.7.4 by selecting a chord on the last beat and choosing Explode. Trace the Explode command's selection handling, then verify that only the selected last beat and the corresponding lower staves are affected rather than the entire bar.