Subgraph Operator is not functional when properties in Blackboard are re-ordered

Steps to reproduce:

1. Create a Subgraph Operator (Right-click in Project Browser > Create > Visual Effects > Visual Effect Subgraph Operator)
2. Open Blackboard
3. Try to drag Min or Max output property to the Properties category. Actual result: The action is rejected and errors are thrown.
4. Try to drag a Range property to the Output category. Actual result: The property does not move to the Output category, but its bubble turns red as if it were in the Output category. More errors appear in the console.
5. Select the Max Output property in the Workspace/Canvas and try to move your mouse. Actual result: It sticks to your mouse. You can get rid of the sticky property by right-clicking.
6. Try to add any node to the workspace by pressing Space. Actual result: No node is added.

Actual results: The Subgraph Operator is unusable when you try to rearrange properties in the Blackboard.

Reproducible with versions: 6000.6.0a8, 6000.5.0a8, 6000.3.17f1, 6000.0.75f1
Not reproducible with versions:
Can't test with versions:

Tested on (OS):

Notes: Errors are linked in the comments