I have been trying to tackle this problem for years but have never understood what the deal is..

On my FiOS DVR, on R/F it sent at least 3 commands to the box, now I am discovering that on my new Mitsubishi DLP it's trying to send at least 10 commands for the directional buttons on IR..

What in the heck can I do to fix this?

You need to reduce the Repeats for the device, go to Devices, Your device, Troubleshoot, Device responds too much or only occasionally, then reduce the repeats.

I have the same RF problem with my both 890's operating a directv HR20-700. In December, Both started behaving badly simultaneously. Worked great for four year.The Directv up down left right recieves two commands. resetting the response setting to 1 or 0 in the troubleshooting setup doesn't help. Shutting down all home wireless applications and systems doesn't help. Reinstalling firmware doesn't help. uninstalling and restalling the device doesn't do any good.

My initial assessment. Software makes installation of devces and activities easy. Hardware is weak.

Try assignig the HR20-700 to a separate port on the RF Extender, using the Extender cables and Covers that  came with the Extender

I started experiencing the same (similar?) problem on November 29th 2012.

I noticed that up and down on my 890 often sent 2 pulses instead of one. When manually using the arrow keys on the front of my HR20-100 I'm able to navigate without the extra press.
I have my remote set to a single RF port, and the IR window is covered with the blaster.

I went into the menu on the HR20-100 and discovered that it had received an update on Nov 28th. Prior to this my system has been working great for ...Years...Basically since the 890 came out, whenever that was :D

Since the update my receiver has also lost internet access (I don't even see it's MAC address in my routers ARP table anymore). I've tried to fix that a million ways, so I might just call DirectTV and replace my admittedly old receiver before tearing into the delay settings on the remote.

Guess the key thing to take away from all this is, DirectTV may have fiddled with RF stuff, and you should go into your delay/repeat stuff and tweak around in there a bit :D