Ctrl+Deleting note on first segment also removes key signature

Issue type

Engraving/interaction

Description with steps to reproduce

Key signature (two sharps in my case) disappear when creating a lead-in measure by removing the first beat.

start a new score, Tenor sax in C (concert pitch) / 4/4 time
tenor sax. has a key signature in D
in the first bar, enter four quarter notes, pitched C
select the quarter note in the first beat
press Ctrl+Del
not only the first note disappears, but also the key signature.

Supporting files, videos and screenshots

before:

after:

In which versions of MuseScore Studio is this issue present?

OS: Windows 11 Version 25H2 or later, Arch.: x86_64, MuseScore Studio version (64-bit): 4.6.2-252830930, revision: github-musescore-musescore-d8d4f8f

Regression

Broken since 4.2

Operating system

Windows 11

Checklist

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• I have attempted to identify the root problem as concisely as possible, and have used minimal reproducible examples where possible