The true trouble is logon.scr. With remote desktop, you don't open a "console" desktop. After few minutes, logon.scr is loaded in memory and kill GPU power. I tryed mstsc /console, but it's continuing to not be a true console with GPU control.
So, the easiest way is to open a session with VNC and disable screen saving. After that, you could open a remote desktop on another account and it's running well.
Thierry.