Magento – Why is ‘sales order place after’ observer not executed in 1.9.1 but it is in 1.8.0

I have created a module for listening to the event sales_order_place_after. I did it following the article http://www.atwix.com/magento/auto-invoice-and-custom-order-status-upon-checkout.

I use it for set my order to processing status, because it's always changed to pending that I set with new order status.

The module works in Magento 1.8.0, but it doesn't work in magento 1.9.1. How could I resolve this problem? Please help me

This is how the module is built:

1. First, I create a module initializer in /app/etc/modules/Atwix_Orderhook.xml with following content

   <?xml version="1.0"?>
   <config>
       <modules>
           <Atwix_Orderhook>
               <active>true</active>
               <codePool>community</codePool>
           </Atwix_Orderhook>
       </modules>
   </config>
   

2. then I create a module configuration file /app/code/community/Atwix/Orderhook/etc/config.xml with content

   <?xml version="1.0"?>
   <config>
       <modules>
           <Atwix_Orderhook>
               <version>1.0</version>
           </Atwix_Orderhook>
       </modules>
   
       <global>
   
           <models>            
               <orderhook>
                   <class>Atwix_Orderhook_Model</class>
               </orderhook>
           </models>
   
           <events>
               <sales_order_place_after>
                   <observers>
                       <auto_invoice_order>
                           <type>singleton</type>
                           <class>Atwix_Orderhook_Model_Observer</class>
                           <method>implementOrderStatus</method>
                       </auto_invoice_order>
                   </observers>
               </sales_order_place_after>
           </events>
   
       </global>
   </config>
   

3. finally I create the app/code/community/Atwix/Orderhook/Observer.php with following content

   <?php
   
   class Atwix_Orderhook_Model_Observer 
   {
       public function implementOrderStatus($event)
       {
           $order = $event->getOrder();
           if ($this->_getPaymentMethod($order) == 'cwinline') {
               $this->_processOrderStatus($order);
           }
           return $this;
       }
   
       private function _getPaymentMethod($order){        {
           return $order->getPayment()->getMethodInstance()->getCode();
       }
   
       private function _processOrderStatus($order){
           $status = $order->getPayment()->getStatus();
           if($status=='SUCCESS'){
               $this->_changeOrderStatus($order);
           }
           return true;
       }
   
       private function _changeOrderStatus($order){
       $statusMessage = 'payment success';
       $order->setState(Mage_Sales_Model_Order::STATE_PROCESSING,Mage_Sales_Model_Order::STATE_PROCESSING,$statusMessage, false);        
       $order->save();
       }
   }
   ?>