Shift+Up & Shift+Down in tab note entry have incorrect effect on linked staves

Windows 7, GIT commit: d65c722

Hard to find a concise way of describing the effect or the situations that cause it, but here are steps:

1) create score for guitar with two linked staves - one standard, one tab
2) note entry mode, type 3 Down 3 Down 0
3) result on standard staff should be G-D-G
4) with cursor still on third line from top, type Shift+Up then Shift+Down

Expected result: G goes to G# then back down to G, so we still have G-D-G
Result: the D is lost, and now we have both a G & G# at the bottom of the chord

Repeat step 4, and now we have three notes clustered toward the top of the staff