On my Diamond, I once used a fast egg hatch code and the manaphy egg code at the same time. It got to the point where if I took one step, the egg would hatch. My game froze every single time the egg hatched, at the same exact point in time. I'm not sure which one of those cheats made it do that, but that's what happened. I was forced to start a new game because I couldn't walk into the pokemon center without the egg hatching and freezing.