I'm having the exact same problem with my 722 ever since L670 was installed around 30 Sep or 01 Oct. The SD picture on Tuner 2 is stretched permanently. I operate my 722 in the Single Mode so that I get both tuners on one single TV. In Dual Mode, Tuner 2 can be sent to a second TV which would operate in SD only. I called Dish and reported the stretched picture to them well over a month ago and they authorized a brand new 722 for me. They agreed that Tuner 2 should not be stretched on SD even though Tuner 2 is an SD tuner only when used in the Dual Mode for a second TV. After I hooked up and formatted the new 722, I called Dish to authorize the new 722 and de-authorize the old 722. They authorized my new 722 and both tuners worked properly for about four hours. The SD picture on Tuner 2 was not stretched and responded from the 4:3 Normal Mode to the Stretch Mode to the Zoom Mode and back to the 4:3 Normal Mode just like it was supposed to. Unfortunately, that didn't last. Four hours after the authorization of my new 722, the SD on Tuner 2 froze in the Stretch Mode just as my original 722 did. BTW, the main tuner, Tuner 1, always operates normally without any stretch on SD.
I immediately suspected that the latest software version L670 was the culprit. L670 was on my original 722 and was now it was on the new 722. After I called Dish again, a new rep agreed that L670 might be the problem and that I should wait for L671 to be downloaded within the week and to see if that doesn't cure the problem. Well, L671 didn't cure the problem and I was pissed. I called Dish back again and still another different rep this time tried to tell me that my TV was to blame and not the 722. He said he had no idea what was going on but regardless it wasn't the fault of the 722. I decided to wait one additional week and I called Dish one more time for an update. This rep, yet still another one, listened to my problem closely and after several tests agreed that my TV was fine and that it was definitely the 722 acting up. He asked me to wait another day until he went home and personally checked both his 722 and 722K. The next day, the same rep called me back and told me that sure enough that his 722 was doing exactly the same thing as mine was doing and also that his 722K was acting normal and was not affected by L670. I felt finally vindicated. We both agreed that the culprit was faulty software and in this case it was L670 that was the culprit. He told me that he would turn in a technical report to the Engineering people and that was about a week ago. I haven't heard anything since.
I don't know how much longer I'm going to be patient with Dish. Their customer service with very few exceptions sucks. I am not going to keep paying them my hard earned dollars for an inferior product. Either they get this problem straightened out or I am gone. I've been with Dish almost 10 years and I like their product. But, I don't like being made to feel like a fool when I report a legit problem and I don't appreciate being ignored while they take their own sweet time fixing this problem that is if they are even fixing it.