just off the scales-real world weights

We are just leaving for a 5 week trip from Chapel Hill NC to Key West, FL.  We loaded the truck and our 173 R Pod and hit the scales at our local county landfill.  I went across the scales 3 times and weighed in different ways.  Here is what we did:

The first time we went across, the weight distribution bars were connected. I weighed with only the truck on the scales, then moved forward with both the  truck and the R Pod being weighed and finally pulled off far enough so the truck was off the scale and only the R Pod was being weighed.

Truck 7500

Truck & R Pod 10660

R Pod  3140

The second weighing was exactly the same sequence except the weight distribution bars were not connected.

Truck 7540

Truck and R Pod  10660

R Pod 3100

The third weight pass was with the truck only-no R Pod attached-7060.

Here is what I think it means:

The truck weighs 7060

The R Pod weighs 3100

Our tongue weight is 7500-7060=440 which is 14% of gross pod weight

Here is my biggest question-- I am confused about the 40 pound differences in the pod and truck weights when weighed with and without the bars attached.  It seems to me that

we are transferring 40 pounds of weight via weight distribution back to the pod from the truck weight-isn’t this backwards? Or is some of the weight distribution involved in the tongue weight?

I  would appreciate any comments about what this means. 

Thanks

Vann