Bugfest. Cannot add tags to Instance when unlinked preceding/succeeding titles present

Overview:

When attempting to add a tag to a MARC-backed Instance that has a preceding or succeeding title entry (780 or 785) that does not link to another existing instance, the UI returns the error:

Cannot save tag data to record. Check that you have the required permissions.

Behind the scenes, this is returned by the API endpoint:

{{{}}
{{ "errors" : [ {}}
{{ "message" : "Instance is controlled by MARC record, these fields are blocked and can not be updated: physicalDescriptions,notes,languages,precedingTitles,identifiers,instanceTypeId,modeOfIssuanceId,subjects,source,title,indexTitle,publicationFrequency,electronicAccess,publicationRange,classifications,succeedingTitles,editions,hrid,series,instanceFormatIds,publication,contributors,alternativeTitles",}}
{{ "parameters" : [ {}}
{{ "key" : null,}}
{{ "value" : null}}
{{ } ]}}
{{ } ]}}
}

If the preceding/succeeding title entry is linked to another Instance, this error does not occur.

Steps to Reproduce:

1. Log into Kiwi-bugfest or folio-snapshot-load
2. Go to Inventory and find an Instance record with source = MARC, and click Edit in quickMARC
3. Add a 780 or 785 field with a subfield $x that contains an ISSN NOT found in an existing FOLIO instance
4. Save, and wait for the Instance to catch up with changes
5. Attempt to add a tag to the Instance

Alternate steps to reproduce:

1. Log into Kiwi-bugfest or folio-snapshot-load
2. Go to Data Import
3. Import the attached file 780 785 examples.mrc using the Default - Create instance and SRS MARC Bib job profile
4. Go to Inventory and view the Instance for Houston/Texas oil directory.
5. Attempt to add a tag to the Instance

Expected Results: The tag should add.

Actual Results: Error message; see above for dev error message, and attached for UI error message

Interested parties: St Vincent College

NOTE Reproduces on Juniper Bugfest, Kiwi Bugfest, and current hosted ref envs. Checked tags on holdings and items associated with the problematic instance, but no problems with them. Only bug is for instances.
charlotte: I reproduced also in Bugfest Lotus