Links to associated test sets, test plans or pre-conditions are removed if associated issues are not synchronized

Steps to reproduce

1. Setup a bi-directional sync for Xray issue types and fields:

   1. Xray Issue Types: Test (or Test Case), Pre-Condition, Test Set, Test Plan

   2. Xray Issue Fields: Tests association with a Pre-Condition, Tests association with a Test Set, Tests associated with a Test Plan

2. Make sure that issues are only synchronized if a certain condition is met, e.g. labels = "public" -> make sure that the field is synchronized as well (bi-directional)

3. Create a test with associations to the other issue types like test set or test plan

4. Set label "public" to the test issue (not to the associated types!)

5. Let test issue sync to the other project

Expected result

The test issue is synchronized to the other project. There, the issue should not have any associations to test sets, test plans or pre-conditions as they are not public yet. However, the internal issue should keep the links to them.

Actual result

Backbone synchronizes the internal issue to the public one but removes the associations on the internal ones.