Form.rb

-semantic_form_for @presenter.sequence, :action => 'update', :html => {:id => 'edit_narrative'} do |s|
  -s.semantic_fields_for :unit, :index => nil do |u|
    -u.inputs do
      =u.input :narrative_sidebar, :label => false,:as => :text, :input_html => {:class => 'mceEditorNarrative'}, :wrapper_html => { :id => 'narrative_sidebar'}
      =u.input :narrative, :label => false, :input_html => {:class => 'mceEditorNarrative'}, :as => :text, :wrapper_html => {:id => 'main_narrative'}
      =u.input :narrative_sidebar_flag, :as => :boolean, :label => "Enable Sidebar:", :wrapper_html => {:class => 'enable_narrative_sidebar'}, :input_html => {:type => "checkbox"}
  -s.buttons do
    =s.commit_button :label => 'Update'

Log

Processing SequencesController#update (for 127.0.0.1 at 2011-02-11 11:29:33) [PUT]
  Parameters: {"sequence"=>{"unit_attributes"=>[{"narrative"=>"<p>r</p>", "narrative_sidebar"=>"<p>qwww</p>", "narrative_sidebar_flag"=>"0"}, {"id"=>"4d13127061dec5b7c5000354", "narrative_sidebar_flag"=>"1"}]}, "commit"=>"Update", "action"=>"update", "_method"=>"put", "authenticity_token"=>"8adrIz3srZfl0AfFEqcCebWWB40SoyzQg07MEpsgGXM=", "id"=>"4d13127061dec5b7c5000355", "controller"=>"sequences"}


###
As you can see, the unit_attributes key is an array, as it should be. What's odd is the checkbox adds another element to the array, as if I was updating 2 units. Also, the ID of the unit is only included in the second element, only the data in the second element gets saved.