Behavior Trees cannot be saved if the Blackboard assigned to it was opened before opening the Behavior Tree from the Content Browser

Behavior Trees cannot be saved if the Blackboard assigned to it was opened before opening the Behavior Tree from the Content Browser.

Reproduced in 4.8.3 binary, 4.9.2 binary, 4.10 Preview 3 binary, and Main (CL 2749677) (not a regression)

1. Open a new project
2. Create a new Blackboard
3. Save and close the Blackboard
4. Create a new Behavior Tree
5. Assign the new Blackboard to the new Behavior Tree
6. Save and close the Behavior Tree
7. Open the Blackboard
8. Open the Behavior Tree from the Content Browser
9. Add a Selector to the Root
10. Save

Result:
The Behavior Tree is not saved. The only way to save the Behavior Tree under these conditions is Save All.