sButtonText not working when extending editor_create

I have the following code, however this results in a Create form with two buttons displaying the text "Create". How do I change this text? Is this a bug?

"oTableTools": {
  "sRowSelect": "single",
  "aButtons": [
    {
      "sExtends": "editor_create",
      "sButtonClass": "editor_create",
      "editor": editorGridMaterialsDT,
      "formButtons": [
        {
          "label": "Create",
          "sButtonText": "Create & Add Another",
          "className": "create_next",
          "fn": function (e) {
            this.submit( function () {
              $('a.editor_create').click();
            }, null, null, false );
          }
        },
        {
          "label": "Create",
          "className": "create",
          "fn": function (e) {
            this.submit();
          }
        }
      ]
    },

Thanks in advance for your help.