Task scheduler runs SYSTEM acc tasks differently?

I want to have Aero Basic theme for console logon only. When I use sethc cmd to run basicthemer on the lock screen, it works just as I want it to, showing basictheme on the lock screen. But when I use task scheduler it has no effect on Windows on the console logon, even though it is running and shows in task manager. And of course, task scheduler works fine for running basicthemer on my user account. Why could this be?