What your doing is trying to parent a prop to itself, so it's no wonder it doesn't work in DS, and tbh I'm surprised it even works in Poser.

In DS 'smartprops' only work at load time and only if you have the figure selected before you load the prop, if you load the prop without the figure selected all you get is a prop and you then have parent it manually, or if you can understand it, by writting a DS script to do the parenting.