Device Detection not redirecting (sometimes)

[e2xperimental]

When I type http://www.union.edu into my mobile browser (Android), the detection script works fine and visitors are redirected to http://m.union.edu.

But if I arrive at http://www.union.edu from a link on another website (e.g. http://www.union.edu/about and click on the "Union" logo) the redirection isn't triggered. Even when I refresh the browser, the page isn't redirected to http://m.union.edu.

I'm using the following PHP detection script, circa November 2011:
https://github.com/espanae/Cascade-Server/tree/master/Kurogo/Mobile-Detect-Redirect

Any suggestions on how to best troubleshoot this are greatly appreciated.