Help... Three zone home

I need some help/ advice prior to discussing this issue with our contractor again. We have a new home with radiant floor heat. We have three zones with a thermostat for each. (Basement, main floor, upstairs)Each level has its own manifold as well which runs three to four loops. It is heated by a Lochinvar Noble combi gas boiler. When having this installed the idea was that each zone would work independently based on its own thermostat. However, I have discovered that when one zone calls for heat we have heat going to all three manifolds/zones. There is a pump for each zone. So as an example, if I go upstairs and bump up my thermostat so that zone calls for heat then go downstairs I will see that our boiler has kicked on and I can feel the pump for the upstairs zone working. So that is good. However, if I go around to the other manifolds each has hot water going through them. Like too hot too touch water. While their pumps don't seem to he actively working its as if they are open and the whole system is receiving heat. Our contractor says they receive "residual" heat from "some" water passing through. However, a friend of ours who also has this same design and setup says this should not be happening. When he has a zone call for heat only that zone is receiving heat and his other manifolds are cool to the touch. The example I gave happens regardless of which zone I bump up. We are in Nothern MI so its not a big deal with regards to the main floor and upper level but with our basement receiving heat every time it is a sauna! Code required us to put down r-15 foamboard which we stapled too and then the whole basement has r-10 foamboard around the exterior so it keeps the heat in extremely well. Any ideas on why all three zones are receiving heat when only one zone calls for it?