Undo of chord symbol edit has no effect

Ubuntu 14.04, GIT commit: 8915f75

1) empty score
2) enter a chord symbol (eg, C7)
3) double click it to edit
4) edit the text (eg, change to D7)
4) undo

Result: nothing. Subsequent undo just undoes the adding of the chord symbol. Undo of other text edits work fine.