windsreen wipers???

[doski]

hey just seein if anyone can cast a light on a prob with the wipers when you turn the wipers on and off again they go across the window twice and when you turn them off they always make another sweep of the window?? starting to get a bit annoying now when they keep dragging across a dry window.............

also what size are the wipers meant to be on the front and the back as i think the ones i have on at the mo are to long coz the blades jump and drag abit ??????