Transpose chordnames always changes to C (0.9.6 regression)

Steps to reproduce bug
1. Open Promenade demo
2. Add "Bb" chordname to a note
3. Edit > Select All
4. Notes > Transpose
5. Press "OK" (without making any changes)

Expected behavior: Chordnames should remain the same

Actual behavior: Chordnames all change to C.

MuseScore version: r.2920 nightly

(Operating System: Windows 7)