Rails multipart form for photo upload does not work

I am tryin开发者_如何学Gog to make my Rails multipart form work for photo upload with jquery-mobile. But the photo params is not being passed to the server. Here is the code, this same code works when I don't include jquery-mobile stylesheeting and javascript

<%= form_tag(posts_path, :multipart => true) do %>
  <br/>
  <%= file_field_tag 'post[photo]' %>
  <%= label_tag 'post[photo]', 'Photo' %>