The Growth Stage Index was reset to 0 instead of the Min_GSI parameter as specified in the parameter table Plant Behaviour. This caused strange behaviour since the Canopy Height Variable is assigned to 0 when the Growth stage Index is less or equal to 0. Providing a perennial plant was simulated that always has has a GSI above or equal to 1 this caused inconsistent estimation of photosynthesis since the Canopy height suddently changed to a minimum value when dormancy was reached in the autumn and remained until emergence (GSI = 1) was reaching in the coming spring. Thanks to Wenxin Zhang that reported the phenomena.