Undo of F2 command does not return tab notes to original strings

Ubuntu 14.04, GIT commit: f78aca0

1) new score, guitar tab
2) note entry
3) 1, right down 2, right down 3, right down 4, right down 5, right down 6
4) at this point you should have the numbers 1-6 running diagonally left-right, top-bottom
5) select those measures
6) F2
7) at this point the last four notes move up a string, as per the usual "lowest fret" algorithm
8) Ctrl+Z

Result: notes return to original pitches, but the last two notes are not on the same strings they started on. It appears the original pitches have been subjected to the "lowest fret" algorithm.

To illustrate: before the F2/Undo, you have this:

After F2 and undo, you have this: