Hi,
Last few days I was working on a page which had lots of list box in it which had multi select option. My master page also had a Menu control for the navigation purpose. One major problem I was facing was with the flickering of the List box as soon as take my mouse over the menu.
As soon as user takes the mouse over the menu all the list box start to flicker. This gives a very bad user experience. Setting the exact height and width and z-index of table and div did not do any good to the flicker. Then and I goggled and found that only way to deal with this issue.
To remove the flickering we have to use the row property and remove any height property in the list box. The row property defines how many rows will be displayed in the list box
<asp:ListBox id=lstExample runat=server Rows=3 selectionmode=Multiple>
</asp:ListBox>
Vikram