Count query with :include generates incorrect SQL

Executing certain ActiveRecord count queries with an :include option provided generates incorrect SQL. For example:

>> Thing.count('widgets.bar_id', :distinct => true, :conditions=>"frobs.name = 'asdf'", :include=>[:widget, :frob])
  SQL (0.4ms)   SELECT count(DISTINCT "things".id) AS count_widgets_bar_id FROM "things" LEFT OUTER JOIN "widgets" ON "widgets".id = "things".widget_id LEFT OUTER JOIN "frobs" ON "frobs".id = "things".frob_id WHERE (frobs.name = 'asdf') 
=> 10

In summary:
"Thing.count('widgets.bar_id', :distinct => true," is somehow getting turned into "SELECT count(DISTINCT "things".id)" and leading to incorrect results.

Note: when a :joins is used instead, everything is as expected.

>> Thing.count('widgets.bar_id', :distinct => true, :conditions=>"frobs.name = 'asdf'", :joins=>[:widget, :frob])
  SQL (0.2ms)   SELECT count(DISTINCT widgets.bar_id) AS count_widgets_bar_id FROM "things" INNER JOIN "widgets" ON "widgets".id = "things".widget_id INNER JOIN "frobs" ON "frobs".id = "things".frob_id WHERE (frobs.name = 'asdf') 
=> 1

(which is correct)

This happens on Rails 2.3.4 and 2.3.5. The rails project is attached.