I've never experienced instability with Poser, but then I never use it for more than preparing single figures for import into Vue.

The reflectivity thing is a pain. It mostly happens when a Poser file uses a reflection map (Poser 4 had no other sort of reflectivity). Vue just ignores this and sets the material to 100% mirror. There's no obvious reason other than laziness; Vue supports reflection maps now, and the Poser material could be converted much more accurately with just a little programming effort.

Breaking the link with Poser by converting to .vob is not a good idea if you are ever going to want to use the same figure in a different pose. Vue is meant to be able to update the figure after it's been reposed, but this feature is not terribly well implemented.