Scaling should be disabled for the testing to get a true 1080p output. If you enable scaling in the nVidia control panel, and then resize the image to fit within your TV's viewing area (if there is overscan, for example) then you're effectively shrinking the resolution. For example, on a TV I had with overscan, to see everything in scaling mode it had to scale the resolution to 1804x996 (shrunk from 1080) so when you scale, you're either losing information or stretching/shrinking and image, depending on the method used.
What happens when 3D is enabled on the ST60, is that for some reason, the TV stretches it left and right even though the TV is receiving a 1080p 3D signal and it should be 1:1 pixel ratio, no reason for the overscan. You can use the driver's software options to scale it back, but you'd then be getting a 1880x1080 resolution instead of the true 1920x1080.