Cant add a removed scene back to the baking set

I showcase the issue in 2 projects. Smaller one is attached.

1) Can be reproduced in any APV project, but optionally open the attached one.

2) Remove a scene from a baking set

3) Try to add it back to the set.

Result: Either nothing happens or an error spawns. Maybe because a dictionary containing the scenes list is not properly cleared.

Expected: The scene is added to the list

Tested on trunk c# code of May 30 + Unity 6000.0.3f1