I got temporarily banned from the Sun Java Forums years and years ago because of something like this. I tried creating a few test accounts and it seemed to be the first name, not even the full name, that was the "match" ! I assume someone on the list had an alias of just "Dave" or "David" and whoever implemented the filter had just done the easiest thing possible.

Not really a life-altering inconvenience, and the other forum members got sufficiently uppity that they re-reviewed it and let me back in, but it was a good lesson in how big orgs have no innate common sense.