Login Behavior, two different sites, but same multisite network

I noticed the following behavior. I have no doubt this is not a bug, and standard WordPress behavior. A little background on setup...

1)Subdomain Multisite Network.
2)Two subsites each with unique logins.

bob.example.om
tom.example.com

For some reason tom ends up on bob's multisite login page (bob.example.com/wp-login.php). Tom attempts to log in to Bob's website with his own (Tom's) login info. The WordPress permissions detect this, and he is denied access, but sees a page with links to his and the main site's dashboard. If he clicks on them he is taken to his own site.

Instead of this behavior, I just want it to reject it as being an invalid username/password combo, instead of forwarding him to the Permissions/Dashboard Link page.

Does anyone know how to do this? Thanks in advance.