You should read the manual for your receiver, and for your BD player.
There is a good chance that the BD player that you have always outputs the 5 volt power via HDMI (
see this), even when off, in which case that is probably why your receiver switches to it. And if your BD player does that, you have 3 choices:
- turn off your HDMI communication between the devices,
- buy a new BD player that does not output this 5v power all the time (which may be hard to find out before trying it), or
- just learn to live with the fact that the receiver is going to switch to BD every time you turn it on.
Such devices that always output 5v, even when off, can cause problems for automatic HDMI switch boxes, as they typically use that 5v as a sensor to determine whether the source is turned on or not.
I personally would do either 1 or 3, assuming that I have correctly diagnosed your issue.
Edited to add:
A simple test of this would be, switch the receiver to something other than the BD, and then when everything is off, unplug the hdmi cable from the BD player. If then the receiver does not switch to the BD input when you turn it on, I have probably diagnosed your issue correctly. If it still switches to the BD input, you need to read the manual for the receiver and see if there is some setting wrong or you may have a defective receiver (but more likely, some setting wrong).