Unmapped Group Doesn't Remove From Customer Portal

Steps to Reproduce:

Scenario A:

1. Create a Service Desk Project
2. Open a new tab and Proceed to the project
3. Edit the Issue Type Scheme that belongs to the project by removing all the existing issue types
4. add in your preferred issue types(eg. Epic) to the Issue Type Schemes.
5. Proceed to Agent Customer Portal in Service Desk
6. Delete all the request types
7. Add a new Request Type with new Group(eg. test)
8. Click the View Customer Portal

Scenario B:

1. Create a Service Desk Project
2. Proceed to Agent Customer Portal in Service Desk and there should be list of Request Types mapped to General group(default)
3. Open a new tab and Proceed to the project
4. Switch the Issue Type scheme to some unique scheme(eg. Agile Scrum Issue Type Scheme)
5. Refresh the Agent Customer Portal and all the request type would be lost.
6. Add a new Request Type with new Group(eg. test)
7. Click the View Customer Portal

Expected Result:

There's no grouping as the request type are mapped to test group. If you have more than 1 group mapped, the group options will show but there should be no group named General.

Actual Result:

The General group are showing in the Customer Portal.

Workaround:

1. Proceed to Issue Type Scheme of the project
2. Add back all the default issue types to the Issue Type Scheme
3. Back to the Agent Customer Portal
4. Remove all the request type that associated to the default group(eg. General)
5. Reconfigure your Issue Type Scheme and remove those issue types again