If the soft jaws are lifting off the bases then either the screws are too long or not tight enough. But are you sure this is what you are seeing? Even when the jaws are firmly bolted down it is possible to see light through at the top and bottom of the serrations because there is a small amount of clearance there.
When the chuck clamps you do get a very small amount of lift from the clearance between the bases and the chuck body. This is why it is a good idea to machine the soft jaws with the jaws clamped against a boring ring so the jaws are lifted in the same manner they will be when in use. A boring ring is just a ring that is clamped on the OD using dowels in the counterbores for the bolts.
An open mind is a virtue...so long as all the common sense has not leaked out.