Rails 3.0 :remote => true with ie9 will double submit form when I clic

I have a Rails 3.0 app which is using a normal :remote => true option for a form_for. It works correctly in all browsers except IE9. Even IE8 works ok. But in IE9, I can see by using the F12 developer tool that it is issuing 2 requests to the server when I click the submit button.

Here's the form_for:

<%= form_for @project, :project, :url => create_project_url, :remote => true do |f| %>

Here's the submit button:

<%= submit_tag 'Create' %>

Looking at the F12 information it shows 1 request initiated by