My Superfish dropdown menu won't show only in IE8 when I hover on the parent items. But when I double-click to select the text of parent item. The dropdown menu will show up. It seems like the screen is not updating when Superfish is trying to render dropdown menu. I also have a picture slider which is doing the animation without any problem, and when the slider is changing(animating), the dropdown menu will appear.
After trying each of my css rules. I found that "filter: ..." for the menu container is not compatible with Superfish dropdown menu animation. After removing the it, dropdown menu works now.