In two screen mode, limit all tethering operations to the second screen while leaving the main screen so normal Library operation can continue.
The intention is that the photographer should be able to use the second screen to trigger the shutter, set presets, and review the image, while on the main screen an "Art Director" can review and select images almost as if tethering is not happening (new images would be available but the main screen wouldn't jump to the just-shot frame).
Secondly, allow a transparent overlay image to permit shooting into a magazine layout.
John