Refused entry with a truck & camper

This makes no sense - we go in easily with our 33,000 pound motorhome - towing a car - no problem. What difference does it make what the registered weight of a pick-up truck is? Wasn't there a long forum post or two about this last year? Wasn't it resolved? How do they get the weight limit - from the registration? Or from looking at something on the actual vehicle? What seems to be the problem? Has anyone ever found out what this is about? Are there crossings where this is not a problem? Last year I thought it had to do with people coming back from Guatemala or Belize. There could be other crossings where this is not a problem but does anyone know where? We talk about how we go to a dentist for cleaning south of Deming, NM and we get our paperwork done there but we do not cross until we get to Laredo. When we do our paperwork there our Bus is 30 miles away and our car is in the parking lot on the US side - we walk in to do the paperwork and they don't seem very concerned. So is it that they look at the vehicle and decide from that or is it that they read something on the paperwork that stops things? Maybe someone will figure out what is going on and come up with a work-around?