Found another "maybe" on preventing the TV from controlling the Receiver's input:
The receiver manual includes a setting for "HDMI Control" under "Network Standby" in the home menu.
Per the manual: "You must adjust the setting of this receiver as well as the connected Control with HDMI-compatible components in order to make use of the Control with HDMI function." ... "When the unit's power is turned off and you have a supported source begin playback while using the Control with HDMI function, the audio and video outputs from the HDMI connection are output from the TV."
Well that's clear as mud, but I would imagine Samsung's "Anynet" = "Control with HDMI." So if this is turned on in the receiver, it might be the culprit. I thought this receiver setting was only for allowing passthrough, but it sounds like this subsetting might also have to do with the issue.
It would really help if the manual didn't describe two settings in almost exactly the same way.
I'll try it this evening!