The user become "email_registration_JRABWYc2oY "

Dear All,
I have enable the module, when I register a new user, My user name change from 'examplename' to "email_registration_JRABWYc2oY". In fact I have receipt two welcome email. I have first receipt: "Account details for examplename at example.com". Few seconds later, I receipt another email "Account details for email_registration_JRABWYc2oY at example.com."

What is the problem for this?? Please help~~~

Thank you all...