Asp.Net mebership creates two users in aspnet_Users table
While using asp.net membership and roles you will see two seperate entries for same user in aspnet_Users table. But you will have a single entry for that user in aspnet_Membership table. The reason for that is you have set applicationName for your membership and roles provider in your web.config.
So if you want a single entry you need to set same value for applicationName attribute for both provider. Yes, this is true if you are using asp.net profile provider.
e.g.
<membership><providers>
<add name="AspNetSqlMembershipProvider"type="System.Web.Security.SqlMembershipProvider, System.Web, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"
connectionStringName="LocalSqlServer" enablePasswordRetrieval="false"enablePasswordReset="true"
requiresQuestionAndAnswer="true"applicationName="/myApp"
requiresUniqueEmail="false"passwordFormat="Hashed" maxInvalidPasswordAttempts="5"
minRequiredPasswordLength="7"minRequiredNonalphanumericCharacters="1"
passwordAttemptWindow="10" passwordStrengthRegularExpression=""/></providers>
</membership><profile>
<providers><add name="AspNetSqlProfileProvider" connectionStringName="LocalSqlServer" applicationName="/myApp" type="System.Web.Profile.SqlProfileProvider, System.Web, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"/>
</providers></profile>
<roleManager defaultProvider="AspNetSqlRoleProvider" enabled="true"><providers>
<clear />
<add name="AspNetSqlRoleProvider" connectionStringName="LocalSqlServer" applicationName="/myApp" type="System.Web.Security.SqlRoleProvider, System.Web, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"/></providers>
</roleManager>
Check this for more information on applicationName attribute.
Reference: