As you might know, when you try to change the wallpaper on ICS (for your homescreen), the OS will ask if you want to set the same wallpaper to the lock screen, and the proper "do not ask again checkbox". By mistake, I pressed it, but I want it back now

Any way to achieve that? 

BTW, I checked the "Clear Defaults" in the Gallery app - nothing. Using Android ICS 4.0.3