Unable to add contributor to a plugin

I added ‘robertpeake’ to the Contributors line of the wp-mvc readme.txt on April 26 (a little over two weeks ago). When I try to add him using the ‘Add Committer’ button on the wp-mvc admin page, nothing happens and a ‘?error=no-user’ query string is appended to the URL (no error message is shown).

It appears that these are the only two steps to add a contributor; am I missing something? One support post says that the turnaround time for the recognition of a new entry in the Contributors line can be about a week, so two weeks seems like it should be more than enough time. Any ideas?