I've seen it happen, here... Mostly on the indoor (regular viewing) antennas.
Here's the deal... to my NW (the same direction the indoor antennas are aimed) are two sheds, with metal roofs, and a large barn, completely covered in metal. Sometimes, a piece of the sheet metal will come loose and flap in the breeze. When this happens the DTV signals can vary, wildly, as the sheet metal waves about. I suspect this is a multi-path issue (with the sheet metal acting as a reflector) that confuses the DTV receivers.
A couple of years ago the barn lost a large metal roof panel. After this happened I had a hard time getting a good signal out of WPSD 32/6 Paducah, KY (30 mi). Again, I suspect multi-path issues as, normally, WPSD is the elephant in the room. Once the missing metal panel was replaced all went back to normal with the DTVs.
Look around your neighborhood... How many metal surfaces do you see?
Another thing that can cause strange signal action...
... is cell site interference.
Look around your neighborhood... How many cell towers do you see?
I've seen light bulbs (usually when they're about to fail) oscillate at UHF frequencies and cause reception problems.
Look around your neighborhood... How many Christmas lights do you see?
As mentioned earlier in this thread, it just may be the TV station has things fouled up. Some of my locals have had problems getting things right.
73, Ed NN2E
Owner / Operator - Murphy's Law Test Site & Thunderstorm Proving Grounds
"You Might Be a Redneck If...
Your TV is on 24/7.
Your TV has been permanently on for over a decade.
The only time your TV is off is during a power outage.
Your TV gets 512 channels, but you go outside to use the bathroom.
Your new TV is sitting on top of your old TV.
Your TV costs more than all of your other furniture.
Your deer-stand has a TV antenna on it.
Your cable provider has no idea that you exist."