Bug with non-ascii characters, quotes and OR operator in search?
This looks like a bug to me too. Here are the search terms and generated queries:

'pølser OR pålegg' -
   SELECT * FROM `craft_searchindex` WHERE (MATCH(`keywords`) AGAINST('pølser palegg' IN BOOLEAN MODE)) AND `elementId` IN (3,18,21,22,23,24)

'"pølser" OR "pålegg"' -
   SELECT * FROM `craft_searchindex` WHERE (`keywords` LIKE '% pølser or %') AND MATCH(`keywords`) AGAINST('+palegg' IN BOOLEAN MODE) AND `elementId` IN (3,18,21,22,23,24)

'"egg" OR "spekemat"' -
   SELECT * FROM `craft_searchindex` WHERE ((`keywords` LIKE '% egg %') OR MATCH(`keywords`) AGAINST('spekemat' IN BOOLEAN MODE)) AND `elementId` IN (3,18,21,22,23,24)