I have verified this bug on android and windows phone but I suppose it is fault of touch detection system.
Well, suppose to use an interface menu composed by windows that slides on screen after player selections (touch). the next window that will slide in, taking place of the old one, will activate UIButtonScale component on each of the sprite, while not being touched, like if it exist a "last touched screen area" memory on NGUI input system that hovers the sprites.
Any idea about how to fix this? On previous version of NGUI i reached this goal commenting OnEnable method on UIButtonScale, but actually [v3.7.3] my fix is not working.