remote_form_for file_field strangeness

Does anyone see any problem with this form?

- form_remote_for(, :html => {:multipart => true, :target => :uploader}) do |f|   .form_element     = f.label :photo     = f.file_field :collateral     = hidden_field_tag :container_id,     = hidden_field_tag :container_type,   .form_element     = f.submit 'Add Photos'

The photo has a paperclip attachment called collateral, and a double polymorphic relation with container (which can be a shoot, model or photographer). At the bottom of the page is an iframe with the id and name 'uploader'. However, when submitted via AJAX, it never serializes the file_field: both the development log and firebug both only show the hidden params being passed. It works fine as a form_for, however.

I'm using 2.2.2 on OSX 10.5.6 and the responds_to_parent plugin to, well, respond.

Thanks, Todd