Comment 5 for bug 1571878

I'm marking this as high because it has the potential for a terribly aggravating user experience through one of our (already unnecessarily complicated) API workflows. The fix involves changing an incorrect 200 response that should not be allowed to a 404 response... and I think that should be allowed because you'll otherwise get the same 404 later in the same API workflow (and too late to do anything about it other than to backtrack).