The exposed filter for combined fileds in Drupal 7 seems to work only when entering the exact casing of the search term or phrase used.  

Seems a patch is required for this:

  1. In your Views, Views Handler Filter Combine – /views/handlers/views_handler_filter_combine.inc, find and change the line below (- indicates the original code line, + replacement code of line)

    -$expression = “CONCAT_WS(‘ ‘, $expression)”;
    +$expression = “CONVERT(CONCAT_WS(‘ ‘, $expression) USING utf8)”;

  2. Clear cache, reload page, test search querying on your exposed filter

Source: https://www.drupal.org/node/1805272#comment-9807743