Drag and Drop Issue - How to make objects that don't have a drop target turn "incorrect" if dropped somewhere

Thank you Tom! That's brilliant :)

I'm going to ask you if you can think of a easy/quick solution to make the incorrects return to state "normal" - or not turning into "drop incorrect" - if they are dragged outside the target before clicking submit, let's say the learner changes her mind. 

What I'm thinking is to create an additional invisible shape that covers the rest of the slide on the left of the target and add a trigger that changes the state of  the incorrects to normal when dragged over/dropped on this new shape. BUT, some spaces around the circle may not be covered (and I also have funny shapes in my real project). 

Or is there an easier trigger I'm not considering. What do you think? :)