Here's the site that I'm working on:
http://www.montevista.dreamhosters.com/
You'll need Opera Mobile Emulator or an Android device (not all of them show this problem). The Samsung Galaxy III shows it as well I think.
Here's an un-minified version of the stylesheet: http://www.montevista.dreamhosters.com/wp-content/themes/Monte-Vista/style-unminified.css
I'm pretty sure that this isn't a problem with the responsive-nav.js, but something to do with my own code. I'm using Skeleton grid.
Is there any testing tool that would allow me to view source on this? I've tried connecting Opera dragonfly but it ends up showing me what is being displayed in the browsers instead of what's in the emulator.
Me again, replying to my own question. I fixed it by switching to Slick Nav (http://slicknav.com/) instead of Responsive Nav.