The BlackboardOverrides are unusable because of shared state in the bb key value pair's PropertyDrawer

[grzes]

Steps:

1. Add 3 blackboard keys to your tree (2 gameobjects, and one other value (Vector3)
2. Add 2 overrides in your tree runner pointing at the tree with the 3 keys
3. When you select 2 gameobject type ones, assigning one assigns the same object to both
4. When changing the first dropdown to the Vector3 key, only the second property drawer changes

Maybe this was working before, but it's now broken on Unity 6.2?

I fixed it moving the
VisualElement pairContainer = new VisualElement();
definition to inside the CreatePropertyGUI method of BlackboardKeyValuePairPropertyDrawer.

(There's another problem that the gameobject key property drawers inside the tree editor window say "type mismatch" when I try to assign them a value, haven't looked into that though)