From the same computer, if two sessions are running simultaneously: one for the normal web browsing and one for the ProxySG administration, there may be an overlap of the usernames.
This situation happens when the web authentication layer and the admin authentication layer use the same realm for authentication.
It is recommended to separate the authentication realms of web access and administration access.
Under Configuration > Authentication > Create a new realm with the same settings as the original one. Use the new realm in the policy's admin authentication layer.