This bug has been in there since beta 1, but I think I have it figured out. When you open an app that is not on your home screen (eg opening Calculator from Control Center when it is placed in a folder), the opening animation is very similar to what we had in iOS 6 rather than the "zoom in on app icon" animation introduced in iOS 7. During that animation, the central icons AND the icon names underneath, all get scaled larger as the icons "zoom" away. It looks like the white splotch you guys are seeing is the tail end of an app name (way zoomed in). The app seems to be located in the second row from the top, second from the left. And, this only happens when the app has a long name (like Google Maps). If you put an app with a shorter name, like Settings, in that spot and repeat, you won't see the white splotch.
Incidentally, you can also get the white splotch problem in the top right of the screen if you put an app with a long name in the second row from the top, second from the right. I hope Apple fixes this bug in a later release. While it doesn't hurt functionality in any large way, it is definitely annoying visually.