environment variables - SystemRoot not substituted

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-admnistratove user, the %SystemRoot% literally remains in the PATH, although the variable SystemRoot has the same value as with Administrator's account.

As a workaround I added the missing directories to the users PATH variable. But I would like to know what causes this trouble and if this can be fixed. Both variables (SystemRoot and PATH) are defined in the non-user-specific "System Variables" set.