I looked at the picture on the box that is in the photo on Amazon's page. In that pic the blue strip is on top and the blades are pointing down. This would indicate that when the blade is mounted on the shaver it needs to be mounted so that the blue strip is being dragged behind the blades. In the case of HB that would mean that the blue strip would be on the bottom. With a conventional razor the blue strip would be on top.
I have Sensor Excels that I was addicted to until I tried the HB triples. They always worked fine so I don't think that the problem is that there is something wrong with the carts. It is strange to mount the blade backward on a razor but with the HB you are actually pushing the blades rather than dragging them as you would with a stick razor. That's why the cart has to be mounted backward.