Cannot add new Keys to a black board if the behavior tree was created first

The user cannot add new keys to the black board if the behavior tree was created first. The user can click add new key and then attempt to select a variable but the variable will not be added.

1. Open the Editor
2. Create a new behavior tree
3. Create a new black board
4. Open the Behavior tree
5. Make sure that the newly made black board is the black board that is being used
6. Click the black board tab
7. Try to add a new key variable to the black board
8. Notice that the variable cannot be added

Expected: The Add new key would add a new variable from the drop down menu
Result: The new variable cannot be added