C# - Membership.DeleteUser (UserName,true) Not Removing User From Role

When I click the "delete" linkbutton, it can delete the all User info from my "UserDetail" table in my "JobPost.mdf", it also delete the corresponding "aspnet_Users" & "aspnet_Membership",but the "UserInRole" still contain that UserName. Even though I specified the Code:Membership.DeleteUser(UserName, true);

I thought true is for bool deleteallrelated data, but it doesn't really delete the userInRole. So next time the user registers with the same name, it automatically get the "admin" role right. This "deleteUser" page I keep it inside a protected "admin"folder. How to solve it? Why Membership.DeleteUser(UserName, true) doesn't delete UserInRole?

protected void GridView2_RowCommand(object sender, GridViewCommandEventArgs e)
{
if (e.CommandName == "Delete")
{
string UserName = e.CommandArgument.ToString();
Membership.DeleteUser(UserName, true);
JobPostDataContext db = new JobPostDataContext();
var query = from u in db.UserDetails
where u.UserName == UserName
select u;
foreach (var item in query)
{
db.UserDetails.DeleteOnSubmit(item);
}
db.SubmitChanges();
FormsAuthentication.SignOut();
}
}
My web.config inside the protected Admin folder:
<configuration xmlns="http://schemas.microsoft.com/.NetConfiguration/v2.0">
<system.web>
<authorization>
<allow roles="Administrators" />
<deny users="*" />
</authorization>
</system.web>
</configuration>