Find_by_contents fails on a complex association

Hello there,
I am experiencing the following problem while using acts_as_ferret.

My user has many posts, but the association between the two models is
rather complex, so I had to go with:

class User < ActiveRecord::Base
  has_many :posts, :finder_sql => "select * from posts blah blah


class Post < ActiveRecord::Base
  acts_as_ferret :fields => [:title, :content]

Now, in the console the following will work as expected:

>> u = User.find(:first)
>> u.posts
>> Post.find_by_contents "blah"

But the following fails:

>> u.posts.find_by_contents "blah"

The log shows that the generated SQL is wrong:

(select * from posts blah blah blah)
AND ( in ('8','5'))

Please note that the WHERE clause in parens is really my entire
:finder_sql. I have not looked into aaf’s code, but it looks as though
it was unable to recognize that my association is completely defined
within :finder_sql, treated it as if it was just a set of :conditions,
and added a SELECT at the beginning.

Am I doing something wrong? Or, is there a workaround?

Thank you all in advance!
Giuseppe B.