Server calls happening twice

Question

I am using ruby on rails at back & javascript on front end to communicate. I am using $.post() / $.getJSON & both of these calls are happening twice ! I am seeing logs of two different calls in server & if I print something in callback function , its printed twice as well.

I am pretty sure its nothing due to my code as even simplistic request function too is showing the same problem.

Could someone help ?

EDIT: Here is sample code which causes problem: controller action:

def index
    @cars = Car.find(:all, :conditions => ['name like?', "#{params[:term]}%"])
    respond_to do |format|
      format.json { render :json => @cars.to_json (:only => [:id, :name])}
    end
  end

JSON call

$.getJSON("/cars", req, function(data) {

                      //create array for response objects
                      var suggestions = [];

                      //process response
                      $.each(data, function(i, val){
                        suggestions.push(val.name);
                      });

                      //pass array to callback
                      add(suggestions);
                    });