The pilot has reported that on the final leg of a competition cross country flight he was forced to make an outlanding. He reported that he flew a full circuit for the selected landing site and completed his checks on the downwind leg. Shortly before touchdown, the glider encountered some turbulence and the landing gear warning horn sounded. The pilot suspected that the landing gear was not fully locked down. To check the landing gear he released the speed brake control from his left hand and transferred that hand to the control column. This allowed him to check the landing gear lever with his right hand. During this transfer of hands he lost control of the glider which impacted the ground and suffered substantial damage. The landing gear was found to be "in-transit" after the glider came to rest. Subsequent investigation by the gliding club showed that the landing gear lever could be moved in its detent such that the warning horn micro-switch operated while the landing gear was still down and locked. It is possible that when the horn operated during turbulence on the approach the pilot moved the gear lever forward which acted to retract the landing gear. The pilot was relatively inexperienced and suggested that when the warning horn sounded he was startled and moved the landing gear lever in the direction he became used to while recently training in the IS-28 glider. This was opposite to the movement required in the Hornet.