sortable screen flickers when on bottom of page

sortable screen flickers when on bottom of page

I developped a page using sortable UI, but when I scroll to the bottom of the page and grab the lowest sortable box, the entire screen starts flickering. I noticed in the examples page:
http://jqueryui.com/demos/sortable/#delay-start

that the same thing happens there when I scroll to the bottom of the demonstration box, so its not a css thing. Does anyone have a solution to this?