By default, SAP NetWeaver Application Server ABAP checks the S_USER_GRP authorization object for activity 01 Create when you try to move a user from one user group for authorization checks to another. To create a distinction between the activity of creating a new user in a user group for authorization checks from moving a user to a new user group for authorization checks, enable activity 50 Move for S_USER_GRP.
This customizing is client-specific.
SAP Note 1663177 SU01: User group as required entry field