MuseScore currently bases the transposition of a score on the Key Signature of the first stave. If the first stave is assigned to an unpitched instrument (typically percussion) the key of C major is assumed regardless of the key of the other instruments.
Comments
To be clear; the only thng that goes wrong is the detection of the original key, which throws off that one operation. Transposition by interval works fine, and the transposition works normally aside from getting the interval wrong in that one case - no corruption, no crash, it's undoable,.etc.
But certainly worth fixing, even if not critical.
https://github.com/musescore/MuseScore/pull/2106
Fixed in branch master, commit 2131b472d4
fix #67836: wrong transposition if top staff is non-pitched
Fixed in branch master, commit 5663b97683
Merge pull request #2106 from MarcSabatella/67836-transpose-drum-key
fix #67836: wrong transposition if top staff is non-pitched
Fixed in branch 2.0.2, commit e6c2d02206
fix #67836: wrong transposition if top staff is non-pitched
Automatically closed -- issue fixed for 2 weeks with no activity.