I don't think a stick spiking problem was the reason. In the previous method, you only needed to have the crosshairs on the same point when you depressed and released the Y key. You did not have to keep it pegged on a spot throughout the calibration.
Obviously, you must know your groundspeed, drop altitude, target altitude and wind direction/speed to make a reasonable drop. Mid-high and altitude drops were not accurate anyway in reality, but having some control over the calibration in AH at least gave us the 'image' of doing something to affect the accuracy of our drops.