I'm never able to undo changes anywhere in the "Find" and "If" tabs. Instead, the last action performed on the rules list is always undone. When ''re''doing the undo, changes made to the removed rule are kept (thank god). Apologies if this is a feature request, because it seems like an annoying bug to me.
Duplicate Create 2 rules numbered 1 and 2 → Add text in either the "Find" or "If" tabs →
Wokaround Fortunately, for now, Ctrl+Y also operates exclusively on the rules list.