I wouldn't characterize it as a glitch, it's the way the game works.
The AI can't drive for sh*t, so every time you look away the game cheats to let them catch up.
It has some bizarre and occasionally funny consequences though (like having them do big jumps in vans, or get them stuck far in-land in boats)
Beware that if you're on a bike and fall you risk getting flattened by a light-speed delivery van
On xbox it won't crash the game (so that must be a bug on PS3).
During the last phase of drug wars (when you have to bring the drugs to the drop-off), you can enjoy reduced traffic and police density (the reduction is a variable of the particular war, so effect varies).