Transpose chordnames makes mistakes with double sharp/flat (0.9.6 regression)

Steps to reproduce bug
1. Open Promenade demo
2. Add a chordname "B#"
3. Notes > Transpose to "B Major / G# minor"

Expected behavior: B# should theoretically change to B-double-sharp, but I don't think double sharps are used for chordnames so it should display C# instead.

Actual behavior: B# changes to B

Discussion: Sibelius displays C# for the chordname (even if double sharps/flats option for notes is marked). My copy of Finale 2007 doesn't seem to transpose chordnames.

MuseScore version: r.2919

(Operating System: Windows 7)