Can't undo accidental parentheses

Steps to reproduce bug
1. Open score with accidentals (such as promenade demo)
2. From the accidental palette drag the parentheses to one of the accidentals
3. Edit > Undo

Expected behavior: Score should return to previous state (without parentheses around the accidental)

Actual behavior: Parentheses remain in place and undo has no effect

MuseScore version: r. 2757

(Operating System: Windows 7)

originally reported by Xavierjazz: http://musescore.org/node/4639#comment-12232