On 7 September 2012, the crew of an Aer Lingus Airbus A320-200 mis-set their descent clearance. When discovering this as the actual cleared level was being approached, the AP was disconnected and the unduly abrupt control input made led to an injury to one of the cabin crew. The original error was attributed to ineffective flight deck monitoring and the inappropriate corrective control input to insufficient appreciation of the aerodynamic handling aspects of flight at high altitude. A Safety Recommendation to the Operator to review relevant aspects of its flight crew training was made.