While I'm not sure about the Orca, some helicopters don't take off straight up without input from the pilot. In other words, it might be intended for you to counter the backwards movement.

(Not up or down voting, just stating the possibility of it being intended).

I'm just going with an assumption here but why would anyone intentionally design a helicopter with a flaw like this?
Wouldn't it be just easier for it to land and take off leveled already, instead of forcing the pilot to make manual corrections?
Maybe it's something common among helicopter designs but in the Orca is much more evident (and annoying) than in others.

Helicopters aren't simple machines. Lose focus for a second and it will roll over and kill you.

In the flight simulator Digital Combat Simulator (DCS) you can fly a very realistic simulation of both the UH-1 Huey and the Russian Black Shark. Both require controller input when taking off or else you will crash withing seconds.

You can trim it out (calibrate the center of the controller input) to avoid having to do this though, something that is not present in ArmA.

Having no experience with flight simulators i'll take your word for it.