The scales appear to be accurate to 10 pounds. That means if even 10 pounds were transferred to the front axle, we should see it. That 10 pounds is 1/185th of the weight of the trailer - less than half of one percent of the trailer weight, or 2.5pct of the pin weight. The hitch would have to be within tenths of an inch of the rear axle center for 10 pounds not to be transferred to the front axle (or off the front axle for that matter).
Maybe more importantly: Isn't a 5th wheel hitch SUPPOSED to transfer some weight to the front axle? It would be almost dangerous otherwise, as any drag on the trailer would actually lift weight off the front of the truck - rotating around the rear axle "pivot". Mounted at or behind the rear axle, a fifth wheel is not a weight distributing hitch. I wouldn't ride a skateboard with both feet centered over the rear axle! Yikes!