Mingle search searches the root form of word instead of the full word because it uses a word-stemming algorithm. If you search for 'savings' , search will search on the reduced form i.e. 'save' and return results that have 'save' or 'saved', in addition to those that have 'savings'. If there is no instance of 'savings', it will return those that have 'save' and 'saved'. Such results should not be interpretted as incorrect. This also means that search results are not limited to exact string matches.
Search will be reworked in the long term and this one should be taken up then.