I believe the new Hacer 90A regulator has what they call "F3A Brake".
I would guess that this function allows the propellor to rotate, but not to "freewheel" quite as fast as it does without any brake on. On my current 90A Hacker regulator, the motor is rotating (windmilling) quite fast on downlines. Maybe the new functionality will make it act more like a 4-stroke, rather than a 2-stroke???
Magne