Allow only one item in each drop target - Not working!

In this project, the user has to drag the photo of each person to its correct location below.

I have set triggers that change each picture to a « Disabled » state when it is dropped on the correct location, so the user cannot move it again, once it is dropped on the correct spot.

I have also set the Drag & Drop Options to « Allow only one item in each drop target ».

It works as expected when I drop items to the correct locations.

For example, if I drag the second photo to its correct location, it becomes disabled and I can’t move it again. This is what I want.

But if I drag another photo on the same spot, it removes the first picture, which returns to its original location and remains disabled, so I can’t do anything with it.

Why am I able to drop multiple items to a same drop target when I specified « Allow only one item in each drop target » in the Drag & Drop Options?

I'm using Storyline 360. See attachment below.