The tool `add existing elements` can add elements "many times" in the diagram

[gcoutable]

Steps to reproduce

1. Create an Action in an Action flow view
2. Display the action flow compartment
3. Add at least one nested Action in the action flow compartment
4. Remove the Action from the diagram
5. Apply the tool add existing elements inside the action flow compartment

Expected behavior

The nested Action is added to the diagram and displayed in the action flow compartment only

Actual behavior

The nested Action is added to the diagram and displayed in the action flow compartment AND on the diagram background