gistfile1.txt

  named_scope :that_are_homonyms, {
    :group => "sensus.label_id",
    :joins => 'JOIN sensus on labels.id = sensus.label_id',
    :select => "labels.*, count(distinct sensus.ontology_class_id) as total", 
    :having => 'total > 1' 
  }

When I do 

bar.foo.that_are_homonyms.size # => 1000s (wrong)

When I do

blorf = bar.foo.that_are_homonyms
blorf.size # => 100s (right)  

Why?

found this: http://www.ruby-forum.com/topic/197436

Also, the reason why Thing.distinct.all.size works is because .all
converts the association proxy returned by the named scope into an
array. Rather than running an SQL query to determine the size of the
dataset, after calling .all it just returns the number of items in the
actual array of data. Since the GROUP is added properly to the actual
data fetch query, .all returns the proper number because that array
has the proper data in it.