Drag drop group state

Hi everyone,
I'm trying to build a Drag&Drop interaction with 1 target and 3 drag groups: GroupCorrect, GroupWrong1, GroupWrong2.

Each group is composed by a text box, a png image and a storyline shape.
The groups have 3 states: Normal (colour blue), Drop correct (colour green), Drop Incorrect (colour red).

I'd like the interaction to work like this:
1) The drag groups have to return to start point if dropped outside any drop target
1) If I move GroupCorrect to the target and submit, GroupCorrect has to turn green
2) If I move GroupWrong1 to the target and submit, GroupWrong1 must turn red, GroupCorrect must turn green, Group Wrong2 must not change
3) If I move GroupWrong2 to the target and submit, GroupWrong2 must turn red, GroupCorrect must turn green, Group Wrong1 must not change

So far I've tried to work with the Drag&Drop basic settings and to:
- add to every object of the group the Drop correct and Drop incorrect state
- remove the text box, keep the png image inside the group and write the text inside the shape
- remove the text box, move the png image inside each state and write the text inside the shape
All of the above doesn't work :(

I've also tried to:
- create custom state
- create 3 invisible additional targets, one for each of the drag group
- create a system of variables to track which answer has been moved last, by combining the interactions of the groups on the real target and the additional target
- I've added in the Correct\Incorrect layers a group of triggers that track these variables and force the custom state change

So far so good, BUT it all goes bonkers when any of the WrongGroups is dropped outside the real target or the additional target. I think the problem is that there is not a way to tell storyline to do something "when a drag group is dropped outside any drop target".

Any idea anyone?