Sounds like a proble with the way you're ejecting the units, and not the paradrop script.
You have to do "unuaasignvehicle _unit" for all of the units that eject, or else they will allways want to get back into the vehicle.
So if you are ejecting unit1, unit2 and unit3 you would need to do something like this:
unassignvehicle unit1
unit1 action["eject",vehicle unit1]
~0.4
unassignvehicle unit2
unit2 action["eject",vehicle unit2]
~0.4
unassignvehicle unit3
unit3 action["eject",vehicle unit3]