Drag and drop (advance)

Hello,

i have problems with interacting my way of checking the answers in drag and drop.

So that i tell a little more about problem. I have chosen 8 variables and give them no as default value. So the point is that if item is dragged on correct spot the value is set to TRUE, if it is dragged on incorrect spot the value is set on FALSE.

As an addition i push user to drag all words on the right place. So if one of value no, the Invalid answer layout appears.

The problem comes when user want to change the word which is already on end place with word on the start square(only one item on each drop targets is checked-because i do not want that happens 2 words ore more on one target) . So it happens that new dragged item has new variable TRUE/FALSE but the item which flies back on starting square does not become value no!

To sum up the main problem is when option only one on drop target is checked, the words which were already on end places does not get value no when they are returned on start position.

I would be very grateful if anyone could help me with the question, i hope that i was clear, if you do not understand please write me. I also attached file of the problematic course.

Thank you