This advice about adjusting my set is all well and good, but I make the suggestion looking at this from a business perspective. I bought my set from a warehouse store, so I don't think I'm going to get too much support for getting a tech in-home to adjust the overscan. And I know what the deal is with the line 21 appearing and it annoys me, but not enough to fight 1001 broadcasters to tell them their equipment they paid money to install in anticipation of 2/17/09 isn't good enough.
This suggestion was prompted by a question from a family member who was visiting me for Christmas. Other people who aren't as much into technology and don't read these forums are probably fuming at a problem they can't solve. I have been a software engineer, and while I am ignorant of the HR2x/H2x software platform, I can imagine that it would be possible to program the receiver to detect such a line and blank it out.
Certainly the lack of this functionality is not a show-stopper, but if it is easy to develop then it could be a way for D* to earn goodwill with customers who don't know or care how television technology works; they are just annoyed by flickering at the top of their HDTV set they paid a lot of money for and want it to stop.