[Plugin: WP-PageNavi] spaces being stripped from query terms on pagination with custom query

Hi guys I’m using wp_pagenavi with a custom query as described here:

http://scribu.net/wordpress/wp-pagenavi/wpn-2-74.html

one of the search terms is freetext, and can contain spaces. If the user searches for a term that contains spaces the first page of results works fine. I can also see the space encoded in the link for page 2 of results (example: http://example.com/school-search/page/2/?s1=sit+amet&x=56&y=10)

however if I click to go to page 2 there is a 301 redirect that strips the space from the search term:
http://example.com/school-search/page/2/?s1=sitamet&x=56&y=10

I’ve seen other people report issues similar to this but can’t find a fix.

Thanks for any assistance!

http://wordpress.org/extend/plugins/wp-pagenavi/