Unexpected behaviour comparing two views of the same data: pp and netcdf

Usecase: I read some pp data, and look at what I have. I then write the same data out to netcdf, and read it back in. I expect the list of cf-fields to be identical. But they are not.

ff=cf.read('myfile.pp`)
ff
[<CF Field: geopotential_height(time(40), air_pressure(9), latitude(1921), longitude(2560)) m>,
 <CF Field: id%UM_m01s30i301_vn1106(time(40), air_pressure(6), latitude(1921), longitude(2560))>,
 <CF Field: id%UM_m01s30i407_vn1106(time(40), latitude(1920), longitude(2560))>,
 <CF Field: id%UM_m01s30i408_vn1106(time(40), latitude(1920), longitude(2560))>]

compare with the same operation aftrer writing that list of fields out to a netcdf file

ff=cf.read('myfile.nc')
ff
[<CF Field: geopotential_height(time(40), air_pressure(9), latitude(1921), longitude(2560)) m>,
 <CF Field: long_name=HEAVYSIDE FN ON P LEV/UV GRID(time(40), air_pressure(6), latitude(1921), longitude(2560))>,
 <CF Field: long_name=TOTAL MOISTURE FLUX U  RHO GRID(time(40), latitude(1920), longitude(2560))>,
 <CF Field: long_name=TOTAL MOISTURE FLUX V  RHO GRID(time(40), latitude(1920), longitude(2560))>]

This is cf.__version__ = 3.16.2

From my point of view the file format should not affect the logical view of the contents. I understand there may be some historical reasons for this behaviour, but maybe they should be reviewed.

Reproduce the PP-to-NetCDF round trip described in the issue with cf-python 3.16.2, then compare the field identities returned by the two reads. Investigate whether the differing long_name and UM identifiers should round-trip consistently; done when the behavior is resolved or its expected semantics are clearly established.