Ok, my 2 penneth, which will be quick as I'm having breakfast. If you look at the shape of the turn as viewed by us i.e. the radio controller pilot guy on the ground, it looks pretty symmetrical. This was mentioned before about trying to make the turn look good for the camera. By doing this with the tail wind present, he's got to lose airspeed halfway through. Bang.
Do this above 8/8 of cloud (as already mentioned) with 15 knots of breeze whilst using a particular cloud for a reference point, you'll be home and dry - your reference point is moving at 15 knots.
I find it hard to believe that wind will affect your IAS. Great discussion tho!
Cheers, DM
Quick edit here - look at the vid, doesn't look like the chopper was out of balance during the turn
And another edit - for the record, I agree that an out of balance maneuver would/could have significant inertia issues.