I registered just for this post with some information I hope you find useful and cool.
So I just bought a new Pioneer receiver and was perplexed why it kept turning on/off with the TV (with a Comcast remote All On button). I tried reprogramming the Aux and also disabling the audio input which I also thought might automatically turn it on. To no avail of course. I then noticed that it would turn on and off just after the Aux light went on so I tried to cover up the remote at that point in the cycle which worked. I confirmed the mysterious 4th signal by recording some video with my cell phone camera which if you didn't know picks up infrared light!
Some background, we have 2 TVs (one HD, one not) and so we have one old light silver remote and one new dark silver/grey remote for the HD set. It turns out that the new grey remote has that 4th signal while the older light silver remote does not. Here is video proof:
New remote (4 signals) [Link: tinypic.com]
Old remote (3 signals) [Link: tinypic.com]

My super-easy solution was to swap out the old remote for the new one and just reprogram the TV button settings. The cable button looks like it's universal for Comcast receivers and works for both. If you don't own an old remote, you might be able to convince Comcast to give you one of their older silver ones.

Peace out.