If you have trouble reading back CV's on the programming track, this may be due to insufficient current draw on the SFX064D function leads.
You can always just re-program the CV value into a CV to get the desired results, even though reading CVs does not work. OPs mode is recommended for programming all CVs except CV01, CV17 & CV18 (2 digit and 4 digit addresses). If a second DCC decoder is present that is not Sound FX compatible then correct readback of CV data is not possible, since the NMRA CV readback was not designed for multiple decoder readback.