V4 uses magnets rather than morphs to adjust the shape of the mesh in response to posing (both to fix places where the joint causes an ugly deformation and to simulate the effect of collar movement on the breasts). The magnetise poses makes those magnets affect the selected item of conformed clothing, so you don't get pokethrough on the top when the collars are raised or on other parts when the limbs are bent (it saves clothing makers from having to add the old JCM morphs). There does seem to be an issue with the poses in D|S 1.8, especially if you have two V4s in the scene. I have a script which will magnetise all the clothing fitted to V4 in one go (run it with V4 selected):

http://www.savefile.com/files/1216562