Just had an interesting problem.
On CableOne, there are SD channels(analog), digital SD channels (480p?), and HD channels. The digital channels are things like Court TV, Hallmark Channel, ...
STB is a Moto DCT6208. Am using the DVI port on the STB to HD1 on a Vizio P50. 4:3 Override is set to "stretch". I am able to switch from Analog SD, to Digital SD to HD without losing a picture. I am able to record from HD, Analog SD or Digital SD and watch the recording.
However, today, as I was recording a channel (a Digital SD channel), I turned on the Vizio to watch the show that was still being recorded from the disk. However, when I turned on the Vizio, no picture. I turned off the Vizio and waited for recording to end, and when I turned back on the TV, nice picture. I am now watching that recording.
(BTW, digital SD much better PQ than analog).