The good news is [a] that there was nothing you did wrong and [b] there is a 'fix' although maybe not ideal.
The bad news is I can't see where the problem is - but there is a problem. When specifying more than 5 menu items anything wider than 170px wide menu boxes breaks the extension. So the temporary fix is to make yours match the dimensions I have used in my version of your menu. And this requires you to re-size the images too. My version is set up, with re-sized images, to 170 wide and it all worked fine. Make the menu boxes 171 wide and it breaks?!?!?
I'll need to dig deeper to find out where and how this is happening but I'll report back if/when I find a solution. In the mean time you will have to work within the 6 times 170px wide constraints.