From past forum posts, it seems that the intention for the “Study” quick action might be to open/study either the last used/opened deck or the current deck.
Given that the default behavior when you open the closed app is to go to the Decks page, it seems to me that the Study quick action would be intended to do something different. So, my interpretation is that behavior #1 is a bug. But, I’m not sure. I’m not sure how the developer intended the function to work.