W7 Administrators

Hello every one!

Does anybody know why domain admin account (which belongs to local Administrator group) may not have the same user rights as local Administrator user account (which also belongs to local Administrator group) ?

For example, the local Administrator group on my W7 PC has two members: the built-in Administrator and DomainAdmin user account. While working as DomainAdmin I type my domain admin's credentials in UAC dialog boxes presented and see the "Access Denied" message.

The question is why DomainAdmin can't do any administrative tasks which the built-in Administrator can?

Moreover, this behaviour continues even after disabling UAC.

Thank you in advance,
Michael