Absolutely correct. Some browsers do treat this differently. When you get to the right side of the menu, just about to touch the sub-menu, the sub-menu will disappear! Sometimes you actually NEED to set a negative number on this (-0.1em;) which will overlap just a hair, but keep sub-menu in view.
Good catch. Thanks. I will also put that in comment section of css

Hey I am having the same problem, it does apear to be margin related...one of the catagories is working fine, the others all disapear when you mouse over to the right on the css menu. Would that be found on the main stylesheet.css or on the stylesheet_catagories_menu.css? Maybe find the code on both?

I am using the Easy Flyout menu, 1.3.8. I finally figured out how to change the colors =) on my version5 site, the version5 site is not having this problem though. Could it be conflicting with Ez checkout? my real store is at realridertack org