Madd Dogg is one of many missions negatively affected by cheat codes. Other examples include:
The Madd Dogg mission is more annoying than them because it appears later in GTA San Andreas. For those that don't know, there is a glitch where the pedestrians attack each other cheat code doesn't properly deactivate.
If one activated it and saved the game, they would find the Madd Dogg mission notoriously difficult to finish. The above YouTube video shows how one has to use several other cheat codes to beat this mission if this glitch occurs.