I had a very similar problem, although in my case it was the (Samsung) UHD Blu Ray player turning on the MU-8000 TV. The short form answer is that turning off AnyNet+ (HDMI CEC) on the Blu Ray is what appears to have fixed it. My configuration is a Marantz receiver, with the Blu Ray, RCN cable box, and TV hanging off it, all connected via HDMI. That allows me to get the best audio from the DVD without the TV recoding it. I have a Harmony remote that I use to control everything. I prefer that to any of the individual remotes because it really can control every function of every device. Shutting off CEC on the TV is not a reasonable solution, because that also disables ARC. I don't know why that should be the case, but at least on this TV, that's how it's set up. That would require me to use an optical cable. That would both require an additional cable and prevent the TV from sending more than two audio channels to the receiver, so no native multi-channel sound from apps running on the TV. However, the problem that I was having was that if the Blu Ray were on, even with the receiver off and pass through and HDMI control turned off on the receiver, the TV would turn on and switch to the Blu Ray source. Whether this happened any given time when turning everything off depended on what turned off first. If the Blu Ray shut down first, everything was OK; if it took longer to shut down than the TV, the Blu Ray would turn the TV back on. What I wanted was for there to be a single controller, the Harmony remote, with the receiver as the hub. That minimizes the amount of audio processing taking place. Having multiple controllers on one system, particularly when there's no one thing that knows the state of the system, is just asking for trouble. Fortunately, turning off CEC on the Blu Ray appears, after multiple rounds of tests, to have resolved the issue for me.
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