Michael,
by default, any user that has admin privileges on the Realm, has full access to channels, regardless of the individual channel ACLs. So if the user that your IS is connecting to UM as, has the Admin API column checked in the Realm > Security > ACL tab in Enterprise Manager, then that would explain what you are seeing.
You can easily disable this admin-override by setting the Realm Config property Global Settings/AllowRealmAdminFullAccess to false. Then the channel ACL will always apply and you should see permission denied exceptions on your IS.
Hope this helps.
#webMethods#Integration-Server-and-ESB#Universal-Messaging-Broker