I too have the problem described by Schecterman. Any object with long, narrow polys, such as a pipe, are ballooned or distorted in render once they become welded to other objects. The same pipe is fine before becoming part of a larger prop. Changing he crease angle does nothing, no matter the setting. Only solution is to turn off smoothing for that prop.

I have even see this happen with items that are not long and narrow, but simply have no poly subdivisions. Such as a box with only 1 poly per side. When merged into another prop, the box balloons in render.

As long as Poser has this flaw, I think it should have a function within the Group Editor to subdivide polys.