standalone UDF and the reference part

I am using Windchill PDMLink Release 13.0 and Datecode with CPS 13.0.0.2 How does Windcill manages the reference between a UDF and its reference part. When a standalone UDF (user-defined-feature) is created within Creo, the user is asked whether to create a reference part: And if he replies yes, a reference part with a _gp file name suffix is saved to disk: But when the UDF is inserted into a target part, and the target part is saved to Windchill, the reference part is not automatically included in the save. It can be added, but there does not appear to be any relation between the UDF .gph model and the reference part. Is there supposed to be a relationship, and if so, is included or excluded based on some Windchill or Creo setting?