picture size

I have just bought a sony RDRHXD560 dvdr with integral freeview. My problem is picture sizing. In some channels the picture is fine and is in wide screen However on some channels it jumps into 4:3 ratio whilst viewing programme but will be in wide screen during adverts. I can rectify this by using my remote control for the tv(a sony 32" widescreen) but this becomes so annoying. Can i do anything to avoid this happening