Sorry about being late to the party, couldn't register yesterday, when I saw your post.
I think the cause of the problem is that E is also bound, by default, to "Fast Forward", I think it's in Vehicle controls. So when you bound it under Helicopter controls, you wouldn't see the Vehicle one (the bind which would apply both to cars & tanks (fast forward), as well as planes and helicopters (fast forward, tipping the nose downwards)).
Just figured I'd add it in all the same, though if the problem's gone now, no problems I suppose.
