`detailed_merge_status` returns `mergeable` when it commits are diverged

Hi! Starting from today something weird happened.

We pushed commit to the base branch and to the head branch as well, and now the merge request has diverged commits, so we shouldn't be able to merge it. The UI shows that properly, that's great.

We're using the API however and it returns mergeable state. Screenshot:

Was this caused by any breaking change today (Feb 9) perhaps?