Quote - It all comes from how the skirt needs to be grouped in order for it to pick up the leg bends. The hip group has a column of polygons that runs straight down the middle of the skirt, to the ground, Same with left and right thigh. It works okay on non extreme bends (usually under 30°), but it's abilities are exceeded in bends closer to 90° .
Just the limitation of Poser's rigging system.

There's a fair amount of this explained in 'secrets of figure creation for Poser 5' book, by B.L. Render.

Yep I know, but sometimes there are breakthroughs, new ways of doing things that no one else ever thought of. Skirts are a particular Dog as far as conforming goes, so I am always looking for a trick that will give me the oppertunity to offer better conforming skirts then with my current method of using ghost parts, and I have yet to find one that doesn't have it's own drawbacks. I know I can offer dynamic skirts but the tradeoff is that you loose a lot of the sculpting you can do with conformers in Dynamics, and there are still a lot of people who's machines just can't handle dynamics quickly enough to be usable.