UAC in domain requires username and password each time

[Tepid]

Something like that,, it's a Token,, not a cookie.

Got a user/pass prompt and it wouldn't accept my domain credentials. I had to use the local credentials.

This is because, (I am assuming here), that UAC is a local PC function, and not a domain function.
Again, I am making assumptions. You are part of the local admin group as a local user on that system, but your domain credentials were not a part of that group. As this is a local PC Function, it is working as described.

Thanks for testing this out.