Undo with multiple selections does not maintain primary selection

[redmunds]

Recipe:

1. Open a file with more than 400 lines (e.g. brackets.js)
2. Place cursors on lines 150, 250, and 200 in that order so middle cursor is primary selection
3. Scroll page so only primary cursor is visible
4. Edit > Delete Line
5. Edit > Undo

Results
Page is scrolled so that last cursor (in page order) is now in viewport. Presumably, this is because the last cursor is now the primary cursor.

Expected
The middle cursor stays the primary cursor.