A later concession would bring difficulties in that the demarcation line between airbrake/landing flaps and performance enhancing flaps is vague. The reluctance within the IGC to allow the later in the Standard Class led to an unsuccessful attempt to codify what constitutes a landing flap. After the LS2 and the PIK-20 exploited this loophole to win the 1974 and 1976 World Championships in the Standard Class, the IGC banned all camber-changing devices from the class and created a parallel 15 metre Class to accommodate them. This decision was polemic as it was the second rule change in a few years and it orphaned several glider types that did not fit well within either class definition (especially the PIK-20 and the Libelle that had been built in large numbers). Notwithstanding, the decision was vindicated by the great success subsequently enjoyed by both the Standard and 15 metre classes.