The reason is to do with the way Poser identifies the fact that there is no displacement map in a shader. It makes VSS think that there IS a displacement map with a name of "No_Map" (or something like that). So VSS creates a Displacement node with a missing map, which causes excessive displacement or extreme puffiness. bagginsbill knows about the problem, but it's apparently not an easy one to fix.

Thus: gods are not omnipotent.

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)