search for: commistion

If I spell "commission" wrongly with an s instead of a t, Xapian (via the QueryParser's get_corrected_query_string function) is finding the right spelling: http://www.whatdotheyknow.com/search/commistion However, if I miss the s out completely, it doesn't find it: http://www.whatdotheyknow.com/search/commision Any idea why that is? Missing the last i out also doesn't work: http://www.whatdotheyknow.com/search/commisson But if I miss the last o out, it finds the right spelling: h...