Just noticed this behavior for the first time and was wondering if this is a feature of bug.
I was doing my Spanish deck, finished all my reviews and started doing my
Russian deck. I did two or three new cards, but decided I didn’t have the time to finish the deck, so I undid them. Once I finished undoing the cards in the Russian deck, Anki took me back to the last card I reviewed in the Spanish deck.
If this is a feature, I think it’s a weird one. If there’s no cards to undo in a deck, I would expect nothing to happen when I use Ctrl+Z.
I’m on 2.1.42.