This happens on both of our TVs (Panasonic and Sony) and our Optima HD projector: when we switch from live TV to OnDemand or back, there is a lose of signal for a couple of seconds and the TVs notify us that there is no signal. It's kind of annoying.
Also, there is an abnormal delay in showing the "You don't have this channel" if we are just channel surfing and happen to land on a channel not in our package.
Is this normal? Should we investigate the signal into the house? I feel that it can't be an HDMI cable issue since all three HDMI cables (different brands and lengths) are having the issue.