Ponder this series of undoable actions:

a. Create object A (existence edit)
b. Select object B (insignificant selection edit)
c. Undo (insignificant selection edit + existence edit)
e. Select object C (insignificant selection edit)
f. Redo (...?)

What should happen? My expectation as a user is that Object A will reappear because I haven't substantially changed any of the actions I've done, but this is not what happens! By selecting a different object in step e, and thereby generating an edit, I cause the undo manager to discard all the edits that have been undone (i.e. the existence edit.)

What should be happening is that the undo manager treats insignificant edits as "interesting edits in the context of a significant edit, but not in and of themselves cause enough for resetting the edit queue." In other words, the undo manager should queue up insignificant edits as they come in and only if a significant edit follows them are they placed in the edit queue. If a "redo" action happens, as in the above case, the queued up insignificant edits are told to "undo" and discarded, and then the edits that in the edit queue, that were previously undone, are told to "redo".