I got on the list to test a private beta of a plugin I'm using on a multisite network.
The plugin authors have code in there to add a custom role. They have a bug that removes the ability to give a user any role except their one custom role.
When I visit
../wp-admin/network/site-users.php, the "Add User" role pulldowns only show the one role this plugin added. The change role pulldown menu shows all the WP default roles, plus a few extra roles this and other plugins have added. If I attempt to change a user to one of these roles, I get a "You can't give users that role" error page.
I've been discussing this with the developer, and they seem baffled.
I've been looking through my database and the codex, and I can't find where the valid roles are defined.