REST hidden_field verb hack and observe_form conflict?

Listers,

I have in routes.rb...

  map.resources :posts, :member => { :preview => :post }

...in posts/_edit.rhtml...

  <% remote_form_for :post, :url => task_path(@post), :id => 'edit_form' ) do |f| %>
     # rest of the form goes here
  <% end %>
  <%= observe_form "edit_form", :url => preview_post_path(@post) %>

What happens is that the routing code receives the hidden "_method=put" field from the serialised form and thinks I am doing a PUT when I am actually trying to do a POST. Needless to say a route to my preview function can't be found and the app barfs out a routing error.

Would you say this a bug in the routing code, the observe_form code or just a nasty usage of the form helper on my part?

-christos