The answer is a simple one: The head you exported from Poser was not symmetrical at export. Did you uncheck all IK first ? Then clicked on ZERO FIGURE before exporting the head? Blenders symmetry function needs a symmetrical obj to start with. When the head is out of symmetry? You get the result you showed. Before starting to create a morph in Blender? Always check that your mesh is symmetrical. Bottom row => Mesh => Snap to Symmetry In the middle of the TOP row you can see how many verts are out os symmetry. The only "cure" is to re-export from Poser with the figure at its "true zero. All Ik removed and figure set to ZERO FIGURE => Then export the vertex group. Once you exported a non symmetrical head? There is NO repair possible because you would export a non symmetrical head, repair it in Blender, and then export it as a morph target into a non-symmetrical figure in Poser shifting the complete head over to one side (or up-down, or forwards-backwards.