Why does my opponent keep driving into a wall?

I was trying to play multiplayer Mario Kart with my sister for our DS's on a long trip and little did she know I had cheats enabled. When the race started everything seemed fine until a little bit later when my sister said she was in first. I thought she was kidding because I was in first on my DS and she was in 8th place, yet on her DS it said she was in first place and I was in 8th.

As looked around the track to find out where she was, I saw her ramming into a wall and turning in circles. That is what confused me. Why does using cheats cause your multiplayer opponents to freak out into walls? What I mainly want to know is if there is any way to stop this from happening and why it happens as well. Thanks!