[Zope] Query Keyword Index unexpected behavior

Hi, all! I'm trying to query a Keyword Index using record attributes. The expression ZCatalog(myindex={'query':['foo','bar'], 'operator':'and'}) should return objects that have both "foo" AND "bar". In my case, no objects with "bar", but with "foo" a lot. The expr above returns ALL objects with "foo". Is it expected behavior? How to get what I really want: the objects with "foo" and "bar", that is None? TIA, -- -tick