Active Record Query cache not working


I have a Rails 2.1 app running on MySQl where the ActiveRecord query
cache is not working for some specific expensive queries they have, and
just for those ones, meaning that in
the same controller action another queries are being correctly cached.

The queries are basically doing a SELECT * from a table, and so far the
only specific details for these non-cached queries that we could observe

  1. They both return a big chunk of text data
  2. The tables they are accessing are in a separate legacy database

About the legacy database, it does not differ that much from the new
one, both are MySql servers and they run in the same box.

Has anyone of you experienced similar problems?