form_for and scopes, rails 3

I have a problem due to scopes and the form_for helper in rails 3. The routes - file looks like this: scope "(/:tab)" do resources :article end The form looks something like this: <%= form_for(@article) %> <%= f.label :title %> <%= f.text_field :title %> etc. <%end%> The tab - attribute is stored in params[:tab], as a string My problem is that this genereate wrong urls in the form. How could I get

[a2ikm]

scopeでルーティングした場合のform_forの引数はインスタンスと:urlオプションを指定