windows 7 - Powershell systemroot in $env:path different when AC elevated

I have a strange behavior with the environment variables at my Windows XP SP3.

When I logon as Administrator, the %SystemRoot% strings in PATH are substituted to C:\WINDOWS, the value of the variable 'SystemRoot' is C:\WINDOWS.

But when I logon as any non-administrative user, the %SystemRoot% literally remains in the PATH, although the variable 'SystemRoot' has the same value as with Administrator's account.

Running PowerShell as a normal user:

PS C:\Users\vic> $env:path (Enter)

%SystemRoot%\system32\WindowsPowerShell\v1.0\;C:\Program Files\AMD APP\bin\x86;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0;C:\Program Files\ATI Technologies\ATI.ACE\Core-Static

Running PowerShell elevated (I right click, run as admin):

PS C:\Windows\system32> $env:path

C:\Windows\system32\WindowsPowerShell\v1.0\;C:\Program Files\AMD APP\bin\x86;C:\Windows\system32;C:\Windows;C:\Windows\ System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0;C:\Program Files\ATI Technologies\ATI.ACE\Core-Static

Env path in Windows:

C:\Program Files\AMD APP\bin\x86;%SystemRoot%\system32;%SystemRoot%;%SystemRoot%\System32\Wbem;%SystemRoot%\System32\WindowsPowerShell\v1.0;C:\Program Files\ATI Technologies\ATI.ACE\Core-Static

Why?