Undoing text insertion seems OK: it removes the last inserted line and redo will then add back that line. However, undoing deletions doesn't seem to work at all. If you add then delete some text, undo won't do anything.
I'm not sure I fully understand how undo and redo are actually working but it seems to me that undo is actually just removing the last line you've added and redo is adding back that line, regardless of what text operation you've actually last performed.
Is there any way to improve this so that it works as undo/redo is usually expected to (i.e. rollback or redo the last edit operation?). I'm not sure how it used to work, but one of our forum users says that the behaviour got worse when we recently upgraded from 1.1 to 1.3.