How badly were the coils iced up. Was the ice uniform and covering all the coil or was the ice covering one or two particular areas of the coils? I ask because, if there are issues with the refrigeration part of the system (low charge, superheat issues, etc.), excessive ice can build up in the areas closest to the expansion valve rather than uniformly across the evaporator. When this happens, since the defrost termination Klixon is located on the opposite end of the coils, the ice nearest the expansion valve will not thaw and, eventually, will keep building up over time.
Once you defrosted the coils and you put it back into defrost, it is normal for the defrost to terminate before the time clock terminates the defrost. As mentioned, that's what defrost termination is supposed to do.