Issue Summary

When moving an issue (e.g Task), that has an epic link, between projects and changing it to sub-task, it keeps the epic link.

Steps to Reproduce

1. Create 2 projects (ProjectA & ProjectB)
2. Create an EpicA and TaskA on ProjectA
3. Add an epic link on TaskA to EpicA
4. Create an EpicB on ProjectB
5. Move the TaskA to ProjectB as sub-task under EpicB

Expected Results

Since the sub-tasks could not have an epic link, when moving the issue, it should remove the epic link.

Actual Results

Epic link is not being removed:

Workaround

Convert the affected sub-task to another issue-type (e.g Task), remove the epic link and convert it back to sub-task.