Warning persists after undoing duplication of the start node in the visual novel sample

Steps to reproduce:

1. Create and open a visual novel director graph
2. Add a start node
3. Duplicate the start node
4. Undo
5. Repeat steps 3 and 4 a few times
6. Observe the console

Actual results: The warnings persist after undoing and you cannot get rid of them

Expected results: The warnings go away when undoing

Tested on (OS): MacOS