I do have a similar problem. We recently updated SB to 1.4.10 to enable CS:GO support. Admins and bans on several servers are managed through SB. SB database is on the same box where TF2 and CS:S servers are. CS:GO servers are on different server.
When I try to enable permissions for an admin on GO servers, nothing happens. admins.cfg is not touched at all. On TF2 and CS:S admins got updated and everything works fine there. But on go servers even sm_reloadadmins and sm_rehash put manually in console does nothing. Once I put admin access in admins.cfg manually. It worked for 1 map. After mapchange, particular admin access from admins.cfg was removed.
Any ideas why it is so?
Edit: problem resolved for me by updating SourceMod to version 1.5.0-hg3665 (linux).