Create two entities.
Crete inheritance relationship between them.
Now the inheritance with normal delete.
Then try to recreate it once again. It seems OK.
Remove it again.
And now try to create inverse inheritance between those entities.
The inheritance will blink and disappear.
It cannot be created, because there already exists at least one inverse (hidden) inheritance.
If it can’t be done because of this, some hint or message box would be nice to explain the situation.
Experienced user can use COMPLETE ALL and delete the old one.
When you completely delete the old inheritance, new inverse inheritance can be made without any problem.