I think it has to do with your display width. Some posts have very wide links or graphics, for instance - on larger displays, there's no jumping around as you scroll through them. But on smaller displays, the wide image forces a horizontal scroll (left or right?), and when you're back to a narrow post, the display settles back down.
The solution is obvious - that new Apple computer with the 30" wide flatscreen display (plus perhaps 2 more screens of the same size). ;->
L.
"You may be disappointed if you fail, but you are doomed if you don't try." -Beverly Sills