I know what you're describing, but don't know how to respond in kind. Empirically, you should fly my Cub in your described scenario to see what happens. As you turn from upwind , through the one-eighty your vector relative to wind direction is constantly changing, as is the attitude (and angle of attack and the wind direction over the wing). This requires an application of power to maintain altitude through the turn, otherwise there is an energy loss from the change in lift during the turn, and the plane loses altitude. Either way, through the acceleration due to gravity or due to the power increase, lift is maintained about the same even though the groundspeed is changing significantly; the overall airspeed over the wing and the lift component is remaining pretty much constant. I can't explain it in the terms I'd like. What I see flying the Cub is a tendency for the bank to increase as I turn cross wind, with the attendent drop in altitude unless I increase power. If I keep power the same, as I complete the turn to downwind, I am in a slight dive, accelerating to maintain lift that I lost turning out of the wind. If I have applied power in the turn, I maintain the altitude and accelerate as I roll out downwind from the increase in power. Either way, once I match the airspeed I had upwind, I have to either level out from the dive or reduce power, or I am going faster, in terms of both airspeed and groundspeed, than I was during upwind flight.

I have actually managed to fly my Cub at almost zero groundspeed (I had about 15 kts headwind). I's kind of scary, you want to think it's going to stall and crash, but as long as you stay directly into the wind, it was okay. Once I got the least bit crosswind, though, it started getting interesting. The big wing on the Cub is really sensitive to airflow, and banking it want to flip it over when the wind gets under the upwind wing.