Opening and closing all the windows w/ the driver side window button

So, I just found out about the feature that allows you to open or close all of the windows by pushing the driver window control as long as the car is off and the door is ajar, but it only seems to work sporadically. The only correlations I have been able to find for when it works or doesn't is that if it doesn't work, I can unlock the doors and it will work. Does anyone know the specific requirements for using this feature? It seems a little silly that it wouldn't work when the doors are locked seeing as how the car automatically locks the doors once you go above 8 mph.