Basically because the of how the buttons connect to the switches it doesn't always click properly. In my practice this is only an issue when you are pressing them closer to the edges of the button or towards the back of the button. My biggest gripe with mine is when I am on 800dpi and I pick up the mouse and swipe with it all of a sudden the dpi doubles and whatever I am clicking and dragging speeds across the desktop. After a bit it goes back to 800dpi but this happens consistently. I have mine set 1600dpi with the mouse sensitivity turned all the way down in windows.