Most of my undos now are for Crown. Maybe when at the times when it could be played as either an Action or as Treasure - with Plaza, last Action/first Treasure, etc - it gives an alert - something like "Crown as Action" vs "Crown as Treasure". I know, extra click. In future versions it could be optional.
I was very confused by this the first time around, because of a log bug on top of the confusion of Crown. If I misplay a Crown as an Action, followed by my treasures, it looks like I played it as a Treasure in the log: "arboretic plays a Crown and 2 Coppers", for example.