JQuery :: Show Funktion And Display None?

Im pretty new to JQuery, but got some things working, but now I came across somthing I cant get to work, even after Googling for some time. In an XSL file I have set an onmouseover event to a function which sets different things on a div, and then displays it accordingly to where the element with the onmouseover is located. I am using JQuery function show("fast") to get a nice animation on the div when its shown. On the onmouseout I hide the div with plain style access with Javascript style.display =none' This is all used for thumbnail showing on a list of elements, but when I stress the system by fast moving over the elements and then suddenly moving the mousecursor away from the list, it possible to get the div to stay shown. I dont really understand why, cause since onmouseout is set display=none to my best knowledge the div should allways be hidden. Is there some kind of delay before show sets the display different from blank, or could someone point me to what im doing wrong.