Problem in ASP.NET Membership Provider using MySQL

Hi,
I am using ASP.NET Membership provider with MySQL Database, Web Form and configured membership using asp.net configuration tool.
When creating one user at a time using CreateUserWizard there is no issue, but when creating multiple users at the same time, some users gets logged in by other user.
For ex. when two users  fill the registration form and at the same time clicks create button, only one user is created but both the users is logged in by the one that is created.
Is there any configuration that needs to be set to handle this issue?
Regards,
Yeou Sunn Liu