Discovery Wings don't actually broadcast anything in widescreen ever.
There has been a bug in L3.2 reported where certain types of STB occasionly start adding black borders down the sides of 4:3 programmes when the box is set to 16:9. I don't know why, and the only fix is to change the settings as you describe.
Of course, most people's TVs are set up to add those black bars anyway, so most won't even notice that the STB is doing it instead. I'm going to take a guess that you noticed it because you view 4:3 programmes in "stretch-o-vision" (which, imo, looks absolutly awful - but that's a different debate!
)
Sorry I couldn't be any more help.