Call :to_model before working with the object.

actionpack/lib/action_view/helpers/form_helper.rb

@@ -1072,16 +1072,21 @@ def error_messages(options = {})
         @template.error_messages_for(@object_name, objectify_options(options))
       end
 
-      def submit(value = nil, options = {})
-        value ||= begin
-          key   = @object ? (@object.new_record? ? :create : :update) : :submit
-          model = if @object.class.respond_to?(:model_name)
-            @object.class.model_name.human
+      def submit(value=nil, options={})
+        value, options = nil, value if value.is_a?(Hash)
+
+        unless value
+          object = @object.respond_to?(:to_model) ? @object.to_model : @object
+          key    = object ? (object.new_record? ? :create : :update) : :submit
+
+          model = if object.class.respond_to?(:model_name)
+            object.class.model_name.human
           else
             @object_name.to_s.humanize
           end
 
-          I18n.t(:"helpers.submit.#{key}", :model => model, :default => "#{key.to_s.humanize} #{model}")
+          value = I18n.t(:"helpers.submit.#{key}", :model => model,
+                                                   :default => "#{key.to_s.humanize} #{model}")
         end
 
         @template.submit_tag(value, options.reverse_merge(:id => "#{object_name}_submit"))

actionpack/test/template/form_helper_test.rb

@@ -521,11 +521,11 @@ def test_submit_without_object_and_locale_strings
     old_locale, I18n.locale = I18n.locale, :submit
 
     form_for(:post) do |f|
-      concat f.submit
+      concat f.submit :class => "extra"
     end
 
     expected = "<form action='http://www.example.com' method='post'>" +
-               "<input name='commit' id='post_submit' type='submit' value='Save changes' />" +
+               "<input name='commit' class='extra' id='post_submit' type='submit' value='Save changes' />" +
                "</form>"
     assert_dom_equal expected, output_buffer
   ensure