Scrolling the window/tab with the autocomplete activated will move the autocomplete window. This works well -- a little too well, since you can scroll the autocomplete past the application as seen here: http://i.imgur.com/FEf2a.png
Also, if I'm scrolling in a window/tab, my mouse stays still while the autocomplete moves. If the autocomplete touches the mouse, the window/tab stops scrolling because the mouse cursor is now over the autocomplete. This is a very minor issue, but I'd prefer that it continue scrolling.
Great work on Sublime, by the way.