When you add structures such as buildings to a mission for MP and play it, the added structures such as concrete walls, barriers and lampposts (even trees) fall over when you die or drive near them. it seems the airflow arround a dieing player asswell as a driving player is the same as landing a chinook :P
ive added a small video demonstrating it.
http://www.youtube.com/watch?v=W-AGsFHqO-A&hd=1
ive also tried to prevent this from hapenning by adding
"this EnableSimulation False;this AllowDamage false; "
to the init of the walls with no success.