Scrolling moves the view up and down / left and right

In 13w24b, when I scroll up or down, my camera is slowly moved up (if I scroll down) or down (if I scroll up), and if I hold shift while scrolling, my camera moves left (if I scroll up) or right (if I scroll down).

I am not sure if this is actually a bug or not. If it is a new feature, I don't like it.