The search results show 20 items per page by default. If a user gets more then 20 items and goes to page 2 of the results list for instance, this page 2 is stored for the rest of his search performances.
For instance if he refines his search by selecting a detail (e.g. "Wiki"), then he gets no results anymore - because there are only 3 entries of Wikis for instance, they should show up on search result page 1 - but the search form remains on the page 2 (which should actually unavailable for 3 results) and does not jump the the beginning of the search results list resp. pages.
Proposal: Every start of a new search clears paging counter, so very new search will show up page 1 of results list.