Creating drop-down - menus too close?

Hi, i am working on implementing a simple horizontal drop-down menu - using the technique from ‘Creating Drop-Down Menus’ by Syko - http://www.kirupa.com/developer/mx/dropdownmenu.htm

My problem is that I want these menu’s to be lined up horizontally, leaving about a 4px gap between each one. If the user moves their mouse across to the buttons to the side, the previous dropdowns seem to stay in the ‘open’ position. The reason for this is that the menu’s are closed when the mouse rolls over the invisible button, however it seems that if there isnt at least 10pixels showing of the invisible button on either side of each normal button, then the menus stay open if you move the mouse too quickly.

Is there any fix for this?

An example is here: http://3amdev.com/tto/prototype1/ - just click the enter button, then the navigation will come up.