Admin group access read/write/admin/delete functions do not work for non-owners of a repository (BB-2727)

When clicking on the admin tab of a project, then modifying "group access", e.g. setting group access to admin, it sends the ajax requests out to modify the settings, but they return 404.

I have attached a screenshot of the group thing, and chrome dev tools showing the failed request.

The specific URL is:
https://bitbucket.org/hit/uc-packages-deb/admin\\
as the user "michaelrose" (who is a part of a group with admin access).