I tried registrering as "simon+redhat" and entered my bug report, and everything looked fine but when I pressed "commit" it complained that "simon" wasn't a registrered user. Registrering as "simon" instead worked...
I didn't have any problems registering as n0dalus+redhat... I do have problems however, with some URLs in bugzilla that don't encode '+' properly (as %2B). An example of this is on my 'Front page', where the link for bugs assigned to me is: https://bugzilla.redhat.com/bugzilla//buglist.cgi?bug_status=UNCONFIRMED&bug_status=ASSIGNED&bug_status=NEW&emailassigned_to1=1&emailtype1=exact&email1=n0dalus+redhat%40gmail.com The + in the url is interpreted (correctly) as a space, so it says it can't find any user with my name. Proper url encoding should fix this.
Red Hat's current Bugzilla version is 2.18. I am moving all older open bugs to this version. Any bugs against the older versions will need to be verified that they are still bugs. This will help me also to sort them better.
I haven't tried to verify the original poster's bug, but the bug I mentioned in comment #1 is still there.
Should be fixed now. The URL in the 2nd comment will need to be recreated though from the advanced query page to take advantage of the fix.