Rails 3.2 jQuery JSONP request not working - Moved Permanently

[Erwin]

I am trying to send a POST request ( 'remove_tag_named' )and getting a simple OK back on success ; it doesn't work.. 

the post is correctly sent , but after then it's looping on sending a GET request to the same url, with the error

301 Moved Permanently 

I should not be far fro the solution, but I am stuck :

In my routes.rb  

      namespace :administration do

        resource :dashboards, :only => :show do

          collection do

            post :remove_tag_named

          end

        end

      end

In my view :

= link_to t(:delete), "#", :id => :delete_tag_link

     #   generated  html =>   <li><a id="delete_tag_link" href="#">remove</a></li>

my js.coffee  script (  # this should be using JSONP I guess )

  $('#delete_tag_link').bind "click", (e) ->

    selected = $('#tags.tab-pane.active #tag-list li span.myTag.selected')

    tagName = selected.html()

    alert 'going remove tag: ' + tagName   # checking I get the correct tag value

    $.ajax 

      url: "/" + locale + "/administration/dashboards/remove_tag_named.json"

      type: "POST"

      dataType: "json"

      contentType: "json"

      data: {"tag_name": tagName }

      success: (result) ->

        selected.remove()

I have also set an init js 

  $.ajaxSetup beforeSend: (xhr) ->

    xhr.setRequestHeader "X-CSRF-Token", $("meta[name=\"csrf-token\"]").attr("content")

and the console output :

[23:18:24.424] POST http://localhost:3000/fr/administration/dashboards/remove_tag_named.json [HTTP/1.1 301 Moved Permanently 46ms]

[23:18:24.491] GET http://localhost:3000/fr/administration%2Fdashboards%2Fremove_tag_named.json [HTTP/1.1 301 Moved Permanently 34ms]

[23:18:24.547] GET http://localhost:3000/fr/administration%2Fdashboards%2Fremove_tag_named.json [HTTP/1.1 301 Moved Permanently 35ms]

[23:18:24.550] GET http://localhost:3000/fr/administration%2Fdashboards%2Fremove_tag_named.json [HTTP/1.1 301 Moved Permanently 48ms]

.........  more GET......