Doug, it's my understanding that rails needs to be prodded to understand your new model definition.
Prodding can be done like this:
class CreateDatabase < ActiveRecord::Migration
class Tab < ActiveRecord::Base; end
#do your create table as usual, then..
Tab.reset_column_information #tell the model to check out it's current/new definition
#then do your Tab.create statements
I use the above technique, and it works like a charm.