Spacer height (and fermata size) not interpreted correctly when opening <4.6 scores with custom staff scaling

Issue type

UX/Interaction bug (incorrect behaviour)

Description with steps to reproduce

1. With version 4.5.2, create a new score, say for two Soprano recorders
2. In each of the staves, change the scale to 200% (NB: I know this is not recommended, but this triggers the bug, at least in part?)
3. Add at least two "Staff spacer fixed down" in the first two systems (as on the GIF).
4. Open the score with version 4.6.2.

Result: the spacers have doubled in height, and so the layout has gone crazy...

Attached .mscz test file created with 4.5.2: Recorders 4.5.2.zip

EDIT: and another test file for fermatas (created with 4.5.2 always): fermatas 4.5.2.zip

Supporting files, videos and screenshots

In which versions of MuseScore Studio is this issue present?

Version 4.6.2 (but I guess already active in 4.6.0?) Same problem with the latest nightly 4.6.3: OS: Windows 11 Version 23H2 or later, Arch.: x86_64, MuseScore Studio version (64-bit): 4.6.3-252940405, revision: github-musescore-musescore-116debc

Regression

Yes, this used to work in a previous version of MuseScore 4.x

Operating system

Windows11

Additional context

First reported on forum here: https://musescore.org/en/node/385853
With additional analysis: https://musescore.org/en/node/385853#comment-1310799

Checklist

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• 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