Use of credentials with UAC in vista

I had UAC turned off. I tried to run a command (eventcreate) under a user's account, from a command prompt with 'run as administrator' privledges, and it failed saying access denied. The user's account has power user permissions. So I logged in as admin and turned UAC back on, rebooted, logged back in as the user, ran the command again, and it prompted me for credentials. So I put in the admin credentials, and it ran the command. Then I logged in as admin, disabled UAC, rebooted, logged in as user, and now it runs the command, whereas before it did not run the command in the user's account. My question is why is it behaving differently now than it was before? UAC hasn't cached the admin credentials, has it? If not, then can someone please explain to me why it now works?

Thanks.

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kapibarra
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