We made a *partial* fix for this, which is online now, but is still not complete. The codes from the aircraft.cfg file are now read and control the ULD, but for the time being, they must match the codes used by GSX, which are not necessarily the ones used by the AFCAD.
For example, American Airlines in GSX is "AA" (IATA), while the atc parking codes usually found in airplanes or AFCADs use the AAL ( ICAO ) so, in your aircraft.cfg, you'll have to set this:
atc_parking_codes = AA
to see ULDs from American Airlines.
However, this will change in a future update, since it's best to conform to using the ICAO standard, like in AFCADs.