I've just noticed this today.
When I click the autocomplete input - the page is immediately scrolled down so that the input appears at the very top (if, off course, the page is long enough to be scrolled).
This behavior becomes really bad on pages that use London-based theme, with it's "always on top" header - when the page is scrolled, the input dissapears under the header.
After some quite long investigation, I think I understood it.
My laptop has touchscreen, that's why I see autocomplete prompt as "Type or tap", instead of "Type or double-click", and also single-click is enough to open the list. And this scrolling behavior is reproduced in case of touchscreen - probably for mobile usability. I have checked with a colegue's computer, and also in IE (there is normal "double-click" behavior in IE - it "doesn't notice" my touchscreen) where it's all fine.
But still, in my case it's a laptop and the screen is big, so I think it's incorrect that the scrolling is based on touchscreen availability, and not on screen size.
Besides, I have checked that the problem with London theme header (mentioned at the start) happens even on mobile.
I don't think this behavior makes much sense anyway. It's probably done to make more space for the list to fit on page, but in mobile (Android at least) this is ensured by the system because the list is docked in the bottom part of page. It should be enough to ensure that the input is fully inside of the visible area, which must be true anyway if you clicked it. And look how dropdowns work - they are fine in mobile and normal mode without any scrolling.
So, can this scrolling be removed?