Persistent Geometry Parameter Read from file Error

Hi,

I am working on a custom parameter component that inherits GH_PersistentGeometryParam (or Param_Geometry), but having trouble reading in the data stored in this parameter after saving it to a gh file. Sometimes the first item in the parameter becomes null for some unknown reason. Even if I strip away all the code in the class(as shown below)and try to save some curves in this parameter, this problem still occurs. I wonder if anyone can share some insight about this. 

Thanks,

Alan

public class Param_ExtendedGeometry2 : Param_Geometry
{
public Param_ExtendedGeometry2()
: base()
{
this.Name = "Extended Geometry 2";
this.NickName = "ExtGeo2";
this.Description = "Extended Geometry Parameter";
this.Category = "User";
this.SubCategory = "Parameter";
}
public override Guid ComponentGuid
{
get { return new Guid("8ae4cf45-9cfc-46b3-91bf-595c05538683"); }
}
public override GH_Exposure Exposure
{
get { return GH_Exposure.primary; }
}
}