All that is happening is that the behaviour tree assigned in a Nested Behaviour Tree State, is always named after the State’s name. If you change the state node name to anything, so will the assigned behaviour tree. This is done to keep naming consinstency.
The node never get’s deleted because of changing names though 🙂 I suppose you just selected back the BehaviourTreeOwner so the NC Editor loaded that behaviour tree back and you though of it deleted? Please confirm.
If you don’t want NC editor to automaticaly change based on selection, you can lock the editor (button on far right in the top toolbar ‘Lock’)
Furthermore the gameobject name is always named after the graph name.