When running in spinup mode and when the last crop in the simulation is a perennial and the perennial is not terminated with a Kill_Crop before the end of the simulation, it appears that the perennial will keep living into the next round of the spinup routine. Attached is an input/output from the online interface where this happened. Notice that the alfalfa is already growing in 1980 at the beginning of the simulation even though it was not supposed to be planted until 2016.
from: @cmw29