Thanks RenegadeMan, you have saved me a whole bunch of typing. I agree completely.
For those that think this is a 'momentum' issue I offer the following:
Momentum is a vector value. The formula is p=mv, p being inertia, m being mass, v being velocity. In our example mass is constant.
Nil wind, aircraft 100 knots, turning through 180 degrees, the velocity change is 100 knots forward to 100 knots in the reverse direction (both airspeed and ground speed), so a 200 knot vector change.
If you are going from a 50 knot headwind to a 50 knot tailwind, the airspeed change is still 100 knots ahead to 100 knots in the opposite direction. So, 200 knots velocity change. If you want to work in grounspeed, it will be 50 knots (100 kts airspeed less 50 kts headwind) to 150 knot in the opposite direction (100 kts plus tailwind of 50 kts). So, the velocity change is still 200 kts, the exact same value as nil wind. As mass is constant and velocity change is the same, the change in inertia is identical in both cases.