When the issuetype Test Set Linked to a Test is changed to Test, the link of the Test is broken (not deletable)

Description
When the issuetype Test Set Linked to a Test is changed to Test, the link of the Test is broken (not deletable)

Pre-conditions

How to reproduce

1. Link Test to a Test Set
2. Move and change the issuetype from Test Set to Test
3. Try to remove the link of the Test Set from the Test.

Actual result/Attachments
Trying to remove the Test Set prompts an error:

Expected result
Should be possible to delete the connection between the Test Set and Test.