Norris Stevens on "Sort only works on first page"

I am using a drop-down to sort posts by title, meta_value, etc. However, the sorting feature only works on the first page. The second page displays the default order rather than continuing the order from page 1. I am using wp-pagenavi for pagination. Any ideas what would be causing this error?

Here's a link to the code:

http://pastebin.com/AwSmMPtM

Thanks so much.