Does not search – am I missing something?

Hi there, I have a fairly simple shortcode form setup.
[searchandfilter fields="search,post_date,media,category" types=",daterange" add_search_param="1" headings="Refine by keyword,Refine by date, Refine by media type, Refine by category"]
I a trying to use this form to modify search results in my existing search.php. When I press submit nothing seems to happen – the search term is not updated. I hacked the plugin and changed the form method from “post” to “get” to see what happens and the search string is
/?ofsearch=hello&ofpost_date%5B0%5D&ofpost_date%5B1%5D&ofmedia=0&ofmedia_operator=and&ofcategory=0&ofcategory_operator=and&ofadd_search_param=1&ofsubmitted=1
Any insight would be greatly appreciated, thanks