I disagree.
I carried out a simple test to see whether that was happening or not.
I took two handy objects and weighed them separately using kitchen scales. Results: loo roll 140g, vase 966g.
I then weighed just myself (80.60) then myself with the loo roll (80.80) then with the vase (81.55) then with both (81.75) and then with neither (80.60).
Clearly trickery of the sort you describe wasn't taking place.