I have the same problem. Found the following bulletin today. Not sure if it applies to this exact issue, as I know there was one other similar issue with GE fridges.
ServiceTechHelp.com :: GE Refrigerators Bulletin, Replacement of Defrost Heater under warranty with Kit # WR51X10101.
EDIT: After looking at the part I am not surte that it is going to help the water line freezing. IF GE will step up to the plate on that issuw why won't they on the water line issue??