Inconsistency between two different role settings for a same user

Under the "site policy by role" settings I've set : "exclude" for the "authenticated user" and "by user" for a custom user role (a subset of authenticated users). Then, on the user account settings of users of that custom role, the checkbox "Disable inactivity automated logout" appears, unchecked, but no automatic loggout is performed. It seems so, that the "exclude" setting has a precedence upon the "by user" setting. If it's the case, the checkbox shouldn't appear on the user account page. Am I right ?

Thanks for your answer.