Yes. They intentionally put something that can potentially ruin your game and make it unusable just for the fans. (+)
Pokémon games that results from a corruption of Pokémon data so that the checksum does not match up with the data's calculations. In Generation IV, sometimes Bad Eggs can hatch into the previous Pokémon, or "----"Bad Eggs are not really Pokémon eggs, and may possibly never have been, but instead the default message returned by the game if the checksum is off (which happens only if data is altered badly). Bad Eggs rarely hatch and cannot be released, merely taking up space, though there are methods of removing them—it is possible to trade a Bad Egg away into another game, or remove it by cheating.
Bad eggs are a glitch in the game, just like Missingno was. It wasn't intentional, but just about every game has its share of glitches. You can't get it perfect.