Scrolling beyond the window edge seems broken

If I put my cursor on the first line of the window and press C-p the behavior is bad. In particular, if you do C-p C-n C-p, then the third keystroke (the second C-p) is not a no-op. Indeed, the first C-p sometimes jumps the window by huge amounts, probably because the standard emacs scrolling logic kicks in. 

Same applies to the last line of the window and C-n.
