I'm able to?

This has nothing to do with the arma3 devs, it depends on the game mode you are playing. If you don't want TKers don't allow random people onto the server, or kick the ones that do..

Yeah, this is not too bad when in the air but when you're trying to land it's a nightmare.

Yes, I've noticed this bug and It has happened straight away for me not after repeating several times.

This is what I did:

Friend was pilot I was in co-pilot seat. He unlocked the controls and I used the take controls option. Flew around for a few moments, handed him back the controls and the helicopters was frozen in mid air for me and other passengers. However the pilot would still see himself as flying.

Yes as I mentioned before you do seem to die now, guess this can be closed. Thanks!

After further testing myself I discovered that you do eventually die however this takes around five minutes.

This is really needed, if your pilot dies you should automatically get control of the airframe, otherwise what's the point in a co-pilot?

Probably because you're at a high speed? I'm almost certain that the rudder is only supposed to be effective at lower speeds.