Mid-measure clef changes do break multimeasure rests, but don't show the changed clef
Muscescore v. 184.108.40.20663
1. Open Musescore
2. File New
3. Score info: blank. Template: Treble clef. Finish. Get 32 bars of rest in 4/4.
4. Drag bass clef onto the treble clef in staff 1.
5. Press M. Rests combine (32) but clef changes back to treble.
If you do this on a score with real music in it, it alters the notes and cannot be fixed by doing a ctrl-Z.