I completely agree with mark_de, for a word processor that is, admittedly, as feature rich and stable as Mellel, not to have the Undo buffer survive a save is absolutely ridiculous. On top of it all, the feature has been requested for years by not a few users. It's a shame, I used Mellel for a while and really wanted to like it—but the lack of persistent Undos was and, sadly, continues to be, a deal breaker.