Bug? Edits by listing owner deletes tags

Hello,

I am having a problem, where if a user edits a listing, (or admin edits a listing using “front end editor”) all tags that were previously added are deleted.

This is a huge issue for the site, since the tags are zip codes served by the business in question, and crucial for the advanced search to work correctly.

I should add that this also happens with all plugins deactivated.

It seems to me I saw someone report a similar problem some time back, but I can’t find it now.