If you try to paradrop Kuma it starts smoking while at it. No damage is done and this only happens in MP. In editor everything works properly.
http://www.youtube.com/watch?v=gm6_kGsVqUM
start test mission on dedicated server
log in and execute on the server side:
_tank = "I_MBT_03_cannon_F" createVehicle [0,0,0];
_para = createVehicle ["I_parachute_02_F", playerServer modeltoworld [0,50,0], [], 0, "FLY"];
_tank attachTo [_para, [0,2,0]];
(where playerServer is your player instance on the server probably (allUnits select 0))
look up and observe smoking Kuma
I've noticed something else. The vehicle leaves track marks on the ground while it is actually on parachute, so that smoke could well be dust from tracks because the engine thinks the vehicle is in fact moving on the ground while on parachute.
Also horizontal velocity is proportionate to the amount of dust, the stronger the wind, the more horizontal velocity the more dust appears.