I had 3 other engineers look into it, and I guess you will have to look for "a more reliable product", but a little research will tell you the more reliable product you will want to look for is the browser.
It appears this only happens with FF 3.6 on MAC when overlapping a flash movie. Several people have reported similar issues we found in google searches, but there isn't a known work around.
I have confirmed that it is fixed in FF 4, which is due out soon, and even worked in FF 3.5 as well as currently works for all browsers on PC and all other browsers on MAC. I doubt you can find another menu solution that gets around the issue, since it would appear to be an issue with the browser and not the html and css that is used for the menu.
Maybe you can find a flash based menu system to get around it, but I don't think another tool will change the limitation of the browser you are running into as long as it is using standard html lists and css. I'm sorry to bear the bad news, but there appears to be no easy solution that we can give you.