I'm testing curious usernames and I am searching their user_id by:

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

I'm trying to get information about this particular user:

http://stackoverflow.com/users/190597/unutbu

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

I know this is a corner case; the only thing I found is the Meta Stack Overflow post A last tribute to the Tilde although I'm not sure if it is related to the same problem.