I believe you will find this is by design. Corporate deployments of Windows 7 are geared towards using KMS servers on the network for issuing and managing license keys.
From what you are saying, it sounds like you are using a standalone MAC key which is linked to the machine it is used on, as parameters such as the system bios serial number become part of the license validation.
You should be able to find out all you need to know about license management on Windows 7 from the Microsoft website.