Unhandled GUI Error when Changing Parameter Scope

Environment:

Windows 10, 64-bit

OpenTAP 9.15.0-rc.3

Steps to reproduce:

1. Be sure to have the Test Automation app installed.
2. Open Test Automation, then add a Sequence Step and a Delay Child.
3. Parametrize Time Delay on Parent (Sequence).
4. Select Sequence and parametrize Time Delay on Test Plan.
5. Edit Time Delay from inside Sequence.
6. Change scope to Test Plan.
7. Confirm with OK.

Actual result:

Unhandled GUI Error occurs.

SessionLog_2021-06-25_16-35-55.txt

Expected result:

Parameter is merged at Test Plan level and is removed from Sequence. No error occurs.