Multiple assignees for merge requests produces confusing results

Refreshing an MR today (specifically https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/10999) showed the "Assignee" field to be empty. I knew it had been assigned to someone, so I scanned the page looking for "unassigned" - I could not find notification that the issue was unassigned.

I then assigned it to myself. The notification then showed that I assigned it, and it was unassigned from the original person.

But clicking on the Assignee "Edit" link, it shows that it's still assigned to two people