"Error: Validation failed: Locations is invalid" will reset subject locations to []

[eatyourgreens]

Came across this today while playing around with updates to metadata for Diagnosis London subjects in subject set 3492, which have text/plain files in the locations array.

Updating a subject without setting the admin flag returns Error: Validation failed: Locations is invalid, which I'm pretty sure is correct because we don't officially support text subjects yet?

Anyway, inspecting those subjects after the failed update, the locations array had been reset to [], which I'm pretty sure is a bug. I had a back up of the subject set data, so I was able to update the subject locations manually in admin mode, but this seems like a dangerous bug for any project that needs to update subject metadata.