Chained Polymorphic Association and the missing type field

I have a chained polymorphic relationship. I will try to describe it
as best as I can.

Imagine:

        Group (polymorphic)
                \
                 >
               Tag (polymorphic)
                   \
                   >
                  Article

The idea being I can TAG many ARTICLES. I can also GROUP many TAGS.
And enjoy using both TAG and GROUP in more creative ways. I also use
proxy classes (GROUPABILITY and TAGABILITY) to encapsulate the
relationships. Both Groupability and Tagability are where
the :polymorphic => true statement resides. Then I use has_many with

        Group
                \
                 > Groupability (real polymorphic)
                 >
               Tag
                   \
                   > Tagability (real polymorphic)
                   >
                  Article

After creating this relationship, the Tagabilty works just fine. The
Tagable_id and Tagable_type field are populated correctly. The
Groupability appears to work fine HOWEVER while the groupable_id field
is populated correctly , the groupable_type field remains nil. I
(believe) I have checked all my syntax which looks correct.

Are there any known bugs with this type of chained polymorphism or
some trick I am missing? Is the belongs_to <NAME> on the polymorphic =
true line, simply appended with "_type" to determine the proper field
in the database to set the value? Is there a manual way of setting the
<NAME>_type field for the proper class? How can I debug this when I am
getting no errors?

Steve Woolley
swoolley@ardentsoft.com