Why is this gap appearing?

Head out to countryshowdown.com and pass your mouse over the links in the navbar. They work! Thing is, on my box, you see this nasty gap (see screenshot) that happens between the navbar and the links.

I'm thinking there's some ninja out there who can look at the discrepancy and go, "That's easy! All you've got to do is..."

Thoughts
Screen-shot-2012-03-16-at-3.52.3.png