This falls in the category of bad luck in having a Pioneer receiver and a Comcast remote.  The red button Comcast is actually a 4 device remote, even though it only has Cable, TV and AUX device buttons.  It also has default setup codes for all 4 devices.  The 4th device (that you don't have control over) uses setup code 1023, which is a Pioneer receiver setup code.  The AllOn button cycles through all 4 devices, sending a power command to each.  So the remote shuts off your receiver, and then turns it right back on again, or vice versa.

The crude way to fix this is to watch the flashing LEDs and just after the AUX light blinks, cover the end of the remote so that 4th signal can't be sent.

Another way is to use the 995 comand to define a macro on e.g. the PIP On/Off button that just has the three devices power signals, and use that instead of AllOn.
Press Setup until 2 blinks-995-Cable-Power-TV-Power-Aux-Power-Cable-Press Setup until 2 blinks.  The last Cable button press is just to put the remote back into Cable mode so it is ready to use after the macro runs when turning on your equipment.

If you only use a restricted set of  receiver functions, you could make lemonade out of lemons by assigning setup code 20490 to AUX, so that it controls most of your BluRay player, but have previously used the 994 command to assign e.g. receiver volume and inputs to buttons on AUX. Then AllOn would toggle power on all 4 devices, and you'd be in control of most functions for all 4 devices.  The idea here is that your receiver won't respond to play, stop, etc, and the Bluray won't be interested in Vol+/- and Mute.  I can explain in greater detail if you're interested.

Edit: changed Audio to Aux, since that's the label on the button.