set completed_at

app/controllers/spree/checkout_controller_decorator.rb

@@ -147,7 +147,8 @@ module Spree
           Rails.logger.error ppx_auth_response.to_yaml
         end
 
-        @order.update_attribute(:state, "complete")
+        @order.update_attributes({:state => "complete", :completed_at => Time.now}, :without_protection => true)
+
         state_callback(:after) # So that after_complete is called, setting session[:order_id] to nil
 
         # Since we dont rely on state machine callback, we just explicitly call this method for spree_store_credits

spec/controllers/checkout_controller_spec.rb

@@ -97,6 +97,7 @@ module Spree
 
           order.reload
           order.state.should == "complete"
+          order.completed_at.should_not be_nil
           order.payments.size.should == 1
           order.payment_state.should == "paid"
         end