All submenus expand on mouseover – don't want that

On my site (c2coe.org/site) all the submenus for the menu expand at once. If you go to projects/project overview you get the whole thing expanding at once making you unable to read or choose anything. I have been looking at this for a while now, but can’t find a reason why. Any thoughts on how to solve this would be very, very, very helpful!