Yes, I know there were a few guys doing them at home at one point. I bought one as it wasn't available retail at the time with the correct code. I didn't know he was printing them himself on sticker paper, quality was rubbish, the size was out, text was not even centrally located and not nearly as cheap as the current stickers. And to top it off it wasn't even the correct code that turned up.
Sounds like you also have a low- quality, dodgy type not sealed or printed on ideal film and probably can't stand engine compartment heat either!