Do you live in a single family dwelling or apartment/condo/town home? I've never heard of a receiver switching to Netflix all by itself.
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That does sound strange. Tuning to some channels will auto-start the app (which I really hate) but the Netflix channel isn't one of them. I've experienced this with the Stingray channels where I tune to it briefly and then switch to a regular channel and the Stringray app, which is extremely slow to load, will kick in while I'm watching the other channel.