Thanks Daniel. You're right some detective work seems in order. I already have done some. First, yes, we're talking about analog cable. Second, these lines run into my condo unit from the distribution rack 10' below my ground floor unit. The outlet I'm having trouble with is the first one in line. It splits from there to the rest of the condo. I guess that the next step is to disconnect the rest of the unit and try the line coming directly from the basement. There are no splitters on the line between the wall outlet and the tv, so the in-wall splitter seems to be the only likely culprit. It seems strange to me though, that the splitter would pass full signal on one leg and filter a single channel on another.

I'll try this tomorrow (I'm at work right now) and post back. I really hope that it's something as simple as a defective splitter.