Sounds like a case of IR interference. Your TV probably has automatic Brightness and/or Contrast control, which uses IR to measure the light in the room.. The IR that the TV sends out interferes with the signal from the remote.
You can google IR Interference and remote for more info, but here's a simple test and solution..
Fold a piece of white paper (printer paper works) in half and stand it up in front of the IR sensor on the receiver (just to the right of the power button, usually), then stand back and try the remote.. if it starts working normally then you have IR interference (The paper acts as a filter).
The solution: Get yourself some Scotch Magic Tape (Yes, that brand and type) and put 2 pieces over the IR sensor on the receiver. This will act as a filter and get rid of the problem. The bonus to the magic tape is that it's virtually invisible so it won't look all hillbilly.