To give you a little background, Poser wants to have a figure (and the clothing is a figure) with parent-child part relations, you can have mutiple children from the same parent but you can't have two children sharing vertexes. Thus pants work well, hip parent, right thigh and left thigh children, but a skirt needs an area defined as a hip between the area defined as thighs, and it screws up the bending. And skirts below the knee are a real problem, as there is no real way to put in shins.