This sounds like HDMI CeC is in play. That is called by Samsung by another name, maybe AnyNet and at times you find it broken. You can try updating all firmware in all devices and hope they fixed it,
I suspect the receiver here since it is the one that can send a command to the TV to switch sources. I can't guess why the receiver is doing that but it would be my first stop for the firmware update. Another fix is to connect the HDMI from the receiver to a non-AnyNet port or disable AnyNet if firmware updates don't fix this.
My Samsung 4G LED 75 inch TV is connected through my receiver which in turn is connected to my Comcast box. While watching cable TV the screen will go blank for a moment and then come on through the TV receiver so I am watching whatever channel through the TV plus the cable channel is also playing (sound only). With the TV remote I hit the return button and a text box pops up on screen asking if I want to leave TV-Plus to which I select yes and I'm back to normal. This process will repeat itself after several minutes of normal watching. This used to not happen and suddenly began going on a month or so ago. Also, I notice the TV alone will turn itself on when I'm not in the room.