Autocomplete window is not aligned with text field when I scroll.

I have a form page with auto complete in a div, the form page is longer
then the size of the div, so we have scroll bar to the form page. when we
type some text on text field
autocomplete window is opened. then if I scroll the form page text field is
scrolled
and the autocomplete window position is not changed. expected position of
the window is with the text field.