As part of Backbone Sync App configuration, the epic ID is linked via edit issue screen's issue link field. This results in the epic link custom field to be populated.
- Edit an issue (click Edit button)
- Add the epic ID in the Issue Link field
- Do a Get Issue REST call to the edited issue
The epic link custom field should not be populated.
The epic link custom field got the value placed on the Issue Link field.
Instead of using the edit issue screen to add the issue link, use "..." > Link