I'm testing curious usernames, searching their user_id by:

http://api.stackoverflow.com/0.8/users/?filter=username_filter

i'm trying to get info about this particular user: http://stackoverflow.com/users/190597/unutbu

http://api.stackoverflow.com/0.8/users/?filter=unutbu
returns nothing.

Any hints?
The only thing i found is this meta post although i'm not sure if it is related to the same problem.