Issue Summary

When you change an Issue Type to a different Hierarchy, we should expect that the Parent link will be completely vanished. However, that is not quite what happens currently. The UI will show the Parent field is empty, however, there will still be some linkages in the back-end. This can be evidenced through the "List" view, as the issues with same hierarchy will be displayed in a different hierarchy level.

Steps to Reproduce

1. Let's assume we have a standard hierarchy - Sub-task, Story, Epic
2. Create a Story - Let's call it TEST-1
3. Create an Epic - Named TEST-2
4. Set TEST-2 as the Parent for TEST-1
5. Now, change the Issue Type for TEST-1, turning it to an Epic.
6. You will observe the Parent field will be cleared, however, when you go to 'List' functionality in your Project Sidebar, the TEST-1 will be displayed under TEST-2 even though they belong to the same hierarchy now.

Expected Results

The Parent link should be completely cleared, which is not happening due to a back-end association.

Actual Results

The issues are still linked through the back-end, resulting in weird scenarios such as the one presented in the 'List' view.

Workaround

Add a new Parent, and remove it afterwards. This action will clear the database association that persisted incorrectly.