HDMI Handshake Issue

That's outside of anything we can do here. I'd make sure that the Yamaha (and the Sharp since it is the sink that generates the initial EDID) have the latest firmware. Obviously turning off the HDMI Control will solve the problem but also eliminate your control mechanism for audio and power.

The only other things I can suggest is 1) a different model of cable box or 2) addding a HDMI switch in between the cable box and the receiver on the off-chance that might fix the Control problem.

Not knowing when your cable box was designed, it is possible that it is working that way by design with HDMI Control enabled.

If you haven't already, there are sections of the AVSForum devoted to each of the three components you own/rent. You might try those forums to see if someone else has run into this problem.

That is strange that HDMI Control is still working afterwards. To be absolutely sure it is disabled, make sure it is "off" in the menus of all of the components, particularly the AVR. I know the Sharp has a menu selection as well. I don't know about the cable box.

Could be an HDCP issue, try installing a Gefen HDMI detective between the receiver and screen.

Sent from my Nexus 7 using Tapatalk 2

So how does copy protection (HDCP) cause the volume control to change the picture for standard def channels?

I know this thread is a couple of months old but I have some information about this issue, though not a permanent solution. I have the same setup, though my receiver may be the 373, can't remember and can't check at this moment. The issue seems to be with the on screen display of the yamaha receiver which I think is displaying in HD while SD content is showing causing the switch. If you haven't already, you'll notice that if you bring up the yamaha menu's the same problem occurs as changing the volume, in other words as I said before, it seems to be with on screen display from the yamaha receiver. A partial fix that I've found is turn off the motorola dvr, hit the menu key and wait a few seconds and menu will come up that lets you change some of the dvr's video settings. Under this menu change the non-hd content setting to "Stretch", hit the menu key again to exit and power your motorola dvr back up and the problem should be gone. The problem now is the setting doesn't seem to stick, for example turning off your yamaha receiver will cause the motorola dvr to revert the settings through I guess some auto detection process, don't know. I saw another thread somewhere with a similar problem that looks like it may have been solved by switching from HDMI to component video, haven't tested this yet personally.

Here's a thread on crutchfield with the same problem, different reciever, stretch setting is lost when the device connected to the DVR is turned off:

http://community.crutchfield.com/TV_Video_Games/f/10/tvs/t/17541/sd-problems-with-comcast-box

The next option is to disable the receiver's OSD if possible. I haven't checked the manual yet but I will look into it this evening.

The only way I've found to disable the OSD on the yamaha receiver is to use component output to the TV however my particular receiver, the RX-V373BL, doesn't allow you to mix inputs and outputs, i.e., HDMI inputs are only output through the HDMI output, component through the component output and analog through the analog outputs so for me this solution is pretty useless. I don't have enough experience with AV equipment to know if this is a technical limitation of all receivers. Looks like the next best solution is to run all devices through the TV and just use the receiver for audio or deal with reseting the DVR settings every time the receiver looses power while the DVR is still on.

It is not a limitation of all receivers. Almost all high-end receivers will convert-up (transcode is probably a better term) particularly with component going to HDMI. None will convert down. So, if you have a component video input, the receiver will also output on HDMI but will not output on s-video or composite. If you have composite that will also be available on component and HDMI. HDMI is only available on HDMI.

Unfortunately, I suspect the cheapest solution to the problem is a different AVR, since when you would be able to get a different DVR is up to the cable company.