After a successfull AJAX validation I'm not redirected where I want

Started GET "/pay_checks?id=1" for 127.0.0.1 at Thu Oct 27 18:09:24 +0200 2011
  Processing by PayChecksController#index as JS
  Parameters: {"id"=>"1"}
  [1m[36mUser Load (0.2ms)[0m  [1mSELECT "users".* FROM "users" WHERE "users"."id" = 1 LIMIT 1[0m
  [1m[35mPayCheck Load (0.3ms)[0m  SELECT "pay_checks".* FROM "pay_checks" WHERE (contract_id = NULL) ORDER BY year
Rendered pay_checks/index.html.erb within layouts/application (16.0ms)
Completed 200 OK in 54ms (Views: 27.8ms | ActiveRecord: 2.2ms)

format.html { redirect_to(pay_checks_url(:contract => @contract_id), :notice => 'Pay check was successfully created.') }

Started GET "/pay_checks?contract=1" for 127.0.0.1 at Thu Oct 27 21:46:09 +0200 2011
  Processing by PayChecksController#index as JS
  Parameters: {"contract"=>"1"}
  User Load (0.2ms)  SELECT "users".* FROM "users" WHERE "users"."id" = 1 LIMIT 1
  PayCheck Load (0.6ms)  SELECT "pay_checks".* FROM "pay_checks" WHERE (contract_id = '1') ORDER BY year
Rendered pay_checks/index.html.erb within layouts/application (21.2ms)
Completed 200 OK in 52ms (Views: 27.5ms | ActiveRecord: 0.7ms)

def index
@pay_checks = PayCheck.all(:conditions => ['contract_id = ?', params[:contract]])
[...]

require 'builder'

class PayChecksController < ApplicationController
  # GET /pay_checks
  # GET /pay_checks.xml
  def index
    #@pay_checks = PayCheck.all
    
    session[:contract_id] = params[:contract]
    @contract_id = session[:contract_id]
    @customer_id = session[:customer_id]
    
    # Prelevo i pay_checks relativi al contratto:
    @pay_checks = PayCheck.all(:conditions => ['contract_id = ?', @contract_id]) 

    respond_to do |format|
      format.html # index.html.erb
      format.xml  { render :xml => @pay_checks }
    end
  end

  # GET /pay_checks/1
  # GET /pay_checks/1.xml
  def show
    @contract_id = session[:contract_id]
        
    @pay_check = PayCheck.find(params[:id])

    respond_to do |format|
      format.html # show.html.erb
      format.xml  { render :xml => @pay_check }
    end
  end

  # GET /pay_checks/new
  # GET /pay_checks/new.xml
  def new
    @pay_check = PayCheck.new
    @contract_id  = session[:contract_id]
  
    # Recupero gli anni validi per la busta paga
    @valid_years = PayCheck.get_valid_years
    
    # Recupero se va aggiunta la tredicesima
    contract = Contract.find(@contract_id)
    
    if contract.monthly_thirteenth == '1' then
      # Calcolo la tredicesima
      @pay_check.thirteenth_instalment = 40.00 # Va poi calcolato il valore vero
    else
      @pay_check.thirteenth_instalment = 0.0
    end

    respond_to do |format|
      format.html # new.html.erb
      format.xml  { render :xml => @pay_check }
    end
  end

  # GET /pay_checks/1/edit
  def edit
    @pay_check = PayCheck.find(params[:id])
  end

  # POST /pay_checks
  # POST /pay_checks.xml
  def create
    # Devo estrarre i valori degli anni anche qui perchè in caso di errore il form viene ripresentato senza "passare" dalla new 
    # Recupero gli anni validi per la busta paga
    @valid_years = PayCheck.get_valid_years

    @contract_id =  params[:pay_check][:contract_id]
    
    @pay_check = PayCheck.new(params[:pay_check])
   
    respond_to do |format|
      if @pay_check.save
      
        # Salvo i permessi
        unless params[:afford].nil? then
              
          # Passo in rassegna tutti i permessi
          params[:afford].each do |key, value|
          #logger.debug("--> #{value[:description]}")
        
            if (value[:paid] == 'true') then
              paid = "1"
            else
              paid = "0"
            end
            
            @afford = Afford.new(:description => value[:description], :hours => value[:hours], :paid => paid, :pay_check_id => @pay_check.id )
            
            unless @afford.save 
              logger.error("Errore")
            end
          end       
        end
    
        # Una volta che il contratto viene salvato aggiorno le info anche sul contratto
        PayCheck.update_contract(@contract_id, params[:pay_check][:advance_tfr])
        
         format.html { redirect_to(pay_checks_url(:contract => @contract_id), :notice => 'Pay check was successfully created.') }
         format.js { redirect_to(pay_checks_url(:contract => @contract_id), :notice => 'Pay check was successfully created.') }
         format.xml  { render :xml => @pay_check, :status => :created, :location => @pay_check }
      else
        #format.html { render :action => "new" }
        format.html { flash.now[:error] = 'Error Saving';  render :action => "new" }
        
        format.js {
          xm = Builder::XmlMarkup.new

           @pay_check.errors.full_messages.each do |msg|
             xm.span {
                 xm << msg
                 xm.br
             }
           end
           
          render(:js => xm.target!)
        }
        format.xml  { render :xml => @pay_check.errors, :status => :unprocessable_entity }  
       end
    end
  end

  # PUT /pay_checks/1
  # PUT /pay_checks/1.xml
#   def update
# Not necessary   
#   end

  # DELETE /pay_checks/1
  # DELETE /pay_checks/1.xml
  def destroy
    @contract_id = session[:contract_id]

    @pay_check = PayCheck.find(params[:id])
    @pay_check.destroy

    respond_to do |format|
      format.html { redirect_to(pay_checks_url(:contract => @contract_id)) }
      format.xml  { head :ok }
    end
  end  
end