Keeping footer nav fixed to bottom of mobile viewport while scrolling content

I have fixed a set of navigation buttons to the the foot of my mobile device viewport and would like to keep these fixed here when the user scrolls content. At the moment however when the user scrolls down the buttons scroll with the page? I have tested this in Android and iPhone 4 and getting same outcome.

Testing this on my desktop browser in chrome + ff etc works fine so is there something different I need to do to achieve this on mobile?

Test page is here: www.kylehouston.com/testing/mobile/

All advice welcome Ky开发者_StackOverflow中文版le

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iOS 4 doesn't have a position: fixed but I think iOS 5 mobile safari does. Fixed positioning in Mobile Safari