A rig crew was running 9-5/8” casing when it became necessary to lay down a joint that had damaged threads. The joint was lowered into the V-door using the top drive and single joint elevators. As the top drive passed the stabbing board it caught the stabbing board extension bending the work platform down. There were no injuries and following a visual inspection of the stabbing board, work resumed. Note that this is similar to an incident that occurred previously.