I've just got a DTR-T2100. No internet connection yet.
It is connected using HDMI to my Sony KDL-32D3000 TV.
When I put the YouView in standby the TV screen goes blank as you might expect, BUT I cannot use the "Input Next" buttons on the TV or the "TV AV" button on the YV remote to switch it to another input (like internal TV tuner or the PVR).
Turning the TV off and back on makes NO difference - just a blank screen and unable to select the input. If I turn the YouView back on I can select an input other than the YouView port and then put the YouView box in standby, but ...