Undo and Redo buttons should show tooltips on what action they will be doing
"Undo "
"Redo "
That is if Bubble can construst a title for each action you do
These textual descriptions of actions can also be useful in the future if you add a History windows like the one in Paint.net (see http://getpaint.net) where the list of all actions is shown and you can select up to a point, removing [temporarily] the next changes in the history and permanently removing the next changes when (and only if) you do a new action that gets inserted in the undo list after the currently selected point (Paint.net shows all items from the currently selected one and back highlighted in the history window and the next ones not). If you just look arround (it’s like a virtual snapshot, it applies all undos but still remembers for redo if you select back to the latest point in the history before you do some edit). Such a history dialog/popup could show via a dropdown button next to the back/forward buttons. Some Office programs (separate dropdowns for undo and redo), Mozilla’s history buttons (those do it on right click) have something similar but don’t show one history list as paint.net, they show other back and forward items as dropdown list under back and fwd buttons to jump to a certain point faster