Bug? With image_select_tag processing in controller?

As I wrote in http://www.ruby-forum.com/topic/69600

A) I created a .rhtml

<%= image_submit_tag(“excel.gif”, :alt => “Download List to Excel”,
:border => 0, :name => ‘render_action’, :value => ‘excel’ ) %>

B) This rendered the valid html

Thus I would expect the value of params[:render_action] to be set to the
value of “excel” in the controller defined by the form tag. But the
parameter render_action is nil. Thus I think that this is a bug in
rails processing of forms. What should I do to progress this.?