Hm, very strange. I can't replicate this on my own iPhone 5, it displays as normal.
Can anyone else with an iPhone 5 check this and let me know how it looks for them? Also, please report your iOS version, if you can.
Your device, Dylan, seems to be ignoring one of the directives that specifies the page width on mobile devices (notice the extra padding to the left of the GTPlanet logo — that should not be so large on a screen of that size). I don't know how this is possible.
Does the problem occur with the header on the homepage, too? What happens when you log out of your account? If you disable the "sticky header" in your account preferences, does this affect the behavior?