Add/Edit MARC Holdings - Adding a new field above MARC 852 results in 852$b value populating the newly added field

This issue is reproduced on MG bugfest and snapshot

1. Add a MARC holdings record

2. Click on the Add field on the same row as MARC 852 

3. Enter a MARC tag and a value in the newly created row. 

4. Move the field above 852 

Expected outcome: The field is moved above 852 and all values in the subfield text box is retained 

Actual outcome: The subfield text box is overridden with whatever is in the 852

NOTE: Can be reproduced when Editing a MARC holdings record 

Screencast: https://watch.screencastify.com/v/kOn0lOhYqKOcrbFbrjEd