umm.. Isn't it supposed to do that? I mean, when you board a vehicle, all the normal actions like 'put weapon on back' and 'weapon M16' and 'salute' .. disapear as well. I think it has to do with the fact that when a unit boards a vehicle,
he seizes to be the unit he was and becomes the vehicle itself. Kind of hard to explain
but anywho, thus the actions which the unit had don't show.
unit has unit's actions like 'salute'
unit boards a truck
unit becomes truck
unit has unit's actions no more
unit has truck's actions like 'engine on'
..
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Oh, and I forgot to mention, that if you want the unit to be able to have the action in the vehicle too, you might have to detect if the player is inside a vehicle (if the player IS vehicle) and then add the action to the vehicle he's in (to the vehicle he IS). That or if your script is some tank smokescreen script, you can add it to the tank itself.
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Forgot to mention one more thing about actions in MP.. it's that the script launched by the action will be executed only on that players machine who activated it.
player1 activates a smoke script
player1 sees smoke
player2 does not see smoke
There's a solution to this, but it's sort of complicated. Can be found by searching this board though.