jQuery UI Dialog cause page jump on open & close on ASP.NET

Question

Hello all,
I have an ASP.NET C# page, with image thumbnails in it.
I created a script that opens a jQuery UI Dialog on each hover on a thumbnail that shows me the thumbnail in larger size in a dialog view, and when I hover out - dialog closes.
My little annoying problem is, that in every mouseover (trigger dialog to open) - the page makes itself 'longer' - a scrollbar appears on the side of the browser, and it seems like the page gets longer when a dialog is openning, but it shouldn't do so.
When I hover off (mouseout) - the dialog disappears and the page returns to its normal state.
Because of this- when I hover through the thumbnails, my page 'jumps'.
I looked for a solution for this, and I've added return false; for each dialog open, and close - and it still doesn't make any different.
Sorry for the unperfect english, and thanks for all helpers!

Answer 1

I finally got my solution - for all interested:

open: function(event, ui){
/*
* Scrollbar fix
*/
$('body').css('overflow','hidden');
}

I added this to dialog's opening event and it fixed the issue!