what a strange case it is?

[farsgsm]

Dear friends.

today i saw some one registered in my forum
his name was the same as mine.

I'm admin of my forum and for example my name is: george
someone else registered as george
exact characters, no more no less.

how is it possible.

i login in my admincp and check the user profile, and saw totally different info
his username was in official usergroup and mine was in admin usergroup

i changed his username successfully and tried to change back his username, and now vb told me that this username can't be choosen because of it's exists.

why vb make this mistake?!! and how?