Hey Damien!
On my spanish deck i have several subdecks. I always go into the parent deck to study. When i then click on study options i can choose between the parent deck and the subdeck of the current card. Theres no way to change my mind on that step, theres no back button. Suggestion: Just make it so, that when i click anywhere else on the screen id go back to the current card.
Also i would find it very useful if i wouldnt just get the parent deck and the current subdeck to choose from, but instead could choose from all subdecks of that parent deck (and the parent deck) there.
Also lets say i want to change the new cards value. I think most of the time people would change it from zero to something else. I think it would make sense if, when it is at zero and i click on it, the zero just got deleted and id be ready to put in the new value without needing to delete the zero. But that is just a very minor change.
And lastly i wondered what would you like better: If id make on single thread where id put all my beta feedback (like we had it in the old forums) or if id make a new topic each time i have something new?
Thanks Damien 
Greetings
Fin