Changing DIRECTV HR24/500 Aspect Ratio

I have tried to change the Aspect Ratio on my HR24 to 16:9, instead of 4:3.  I can change it on the TV Ratio screen, but after I leave that screen and choose TV Ratio again, it flips the ratio back to 4:3 by itself.  It will not allow my change to 16:9 to stay as I choose.  What is going on??