Undoing fret mark change restores it to wrong string

1. Create 4-string bass tablature score.
2. Enable 'Note Entry'.
3. Click on third string.
4. Press 7.
5. Press 4.
6. 'Undo'.

Result: The fret mark is the same note, but on the wrong string (String 2 and fret mark 2).

Using MuseScore 2.0 Nightly Build 1812015 - Mac 10.7.5.