Jffsieg,
It's because the player team are in a vehicle in the begining.
I usually solved this problem: in the begining the player and his group NOT in the vehicle. And in the init.sqs insert these code:
~0.01
{_x moveInCargo vehicle} forEach units group player
The 0.01 sec delay is enough for the ArmA to this group NOT in the vehicle in the briefing phase, but after briefing they ARE in the vehicle.