I’m afraid the issue is not related to this plugin. I have tested by de-activating the Ajax Search Pro and tried the given URL but the problem was still there.
The URL you provided is definitely not generated by ajax search pro: http://tripical.com/?toursearch=1&s=&tourtax%5Bpa_location%5D=iceland&tourtax%5Bpa_duration%5D=&tour_category=
It looks like it might be a part of the filter below the search bar, which is a different plugin. (product filter I guess?)Best,
If you like my products, don't forget to rate them on codecanyon :)