No idea why it's that way. Scaling should not change the polys. In Poser, unless I'm very wrong, scaling is a relative value to the Poser universe. Perhaps it doesn't return to it's relative presets after each import. If you imported in pieces, rebooting the app. after each import we might get an answer. I had a strange one not long ago. I imported the same piece twice in the same scene and they were different size relative to each other. Rebooted. Tried again and it worked ok. I thought, wow! I must have made some mistake in importing. But I guess, what's happening is, instead on scaling the object itself, it's the P universe that changes in relation to the object. The object remains the same.

Un coup de dés jamais n'abolira le hazard
S Mallarmé