1.Add a trigger in the editor, area 1000-2000, place 50 OPFOR units in it.
2.Place a blufor helicopter far away, and player as driver.
in the trigger's condition: vehicle player in thislist (above, put anyone or blufor and present; or you can also group the trigger with the player's vehicle).
3.In activation: hint "hello world".
4.Fly until the trigger's area, but do a save 100m before you get in.
5.Get in and load, many times, you'll see that you don't get each time the message.

It's very important that the triggers work again, because at the moment, it's not possible to trust them, I think. It's too randomly...

Edit: the problems is probably mostly with choppers, and maybe also, there's a problem with the chopper's position, when it comes in the area and is inclined at the same time. Difficult to know exactly when the problem appears.