I don't know if there's an answer to this,It might just be a limitation of the model.
I've been trying to pose M4 with his skeleton and muscle maps and transparencies to use as references for a project. I'm pretty new to Poser so bear with me.
First off and this may be of some use to other newbies, it took me quite a while to work out how to get the M4 skeleton to move in unison with Micheal 4. Move Michael and the skeleton stayed where it was or vice versa. No amount of 'Parenting' Setting or changing figure seemed to solve the problem. I may well not have been doing this correctly or going down the wrong route entirely but in the end all I manage by this method was to get the two figures to rotate in unison along x y or z  axis and that was it.

Solution - load Michael, load M4 Skeleton, choose Conform to from the Figure menu (which for a moment makes the skeleton' knees stick out and you think you're on the wrong track) Follow this with Zero Figure, again from the Figure menu and you're back on track  and you can go ahead and load up muscle maps and a transparency for the muscles and there's your skeleton visible through the muscles and it all moves as one. So far so good.

There are some limitations to the poses. One is quite understandable. I imagine  a fully articulated vertebra by vertebra spine wasn't really feasible on this sort of model so bend him too far and Michael gets breaks in his spine. I can live with that,he still looks pretty good,very usable for all sorts,great for working out poses and sketching from for starters and for final images.

After all that waffle ,here's my question. When I try to move the lower jaw, regardless of whether I move michael's jaw or the skeleton's jaw,the skeleton's jaw always moves and Michael's mouth remains resolutely shut. Is there a solution to this or is it just a limitation of the model or a bug even? I can live with it,just wondering if there's a solution.There may be a few other little quirks like this that I haven't found yet,perhaps in facial morphs as a whole and if there's a solution perhaps it applies to all.
Any thoughts much appreciated.

Anatomically, the jaw movement is correct.  Close your mouth and open your jaw, you will find that your mouth will remain closed to a certain extent. 

The knee jerk upon conforming is do to IK being active for the feet.  To prevent that in the future, just turn off IK for all limbs.

Ah  I haven't described what I mean properly. I understand what you're saying about the jaw being able to move without the mouth having to open but If I open the jaw on the skeleton or on Michael it's always the skeleton's jaw that moves and it breaks through the bottom of Michael's  jaw so to speak, it pokes through,micheals  jaw doesn't appear to move at all.  I was expecting Micheal's mouth to open, and the skeleton jaw with it if I dialed enough in but they don't move in unison at all if that makes any sense.

Got you on the IK. Thanks I'll turn it off.

Edit - Hmmm no, just tried that and even with IK off on Micheal the knees still poke through until I zero the skeleton.

Michaels mouth is morphs of the head. I dont think the lower jaw is connected to any of the morphs as a master. You would need to position them individually.

Once you conform the skeleton to M4 you should not need to move it at all. Just move M4 and the skeleton should move with it.

Yes M4 and the skeleton are moving around fine together now. I see what you're saying,it's down to fine tuning as regards the head. Morph his mouth and then adjust the skeleton jaw to match.Obvious now that you say it.I was expecting the head to conform in the same way as the rest of the figure which now that I think about it, considering how much detail and movement there is in the face makes no sense at all.Thanks for that.

Edit - Just gave that a run through, works a treat, Michael 4 he say "Ah!"

Poke throughs are unavoidable, sometimes.  In this particular case, we are not really conforming a piece of clothing, we are trying to conform 2 complete figures within each other.

And I suppose that's more than likely if the one on the inside is less flexible than the one on the outside. In this case as a for instance the spine pokes through at the top of the neck  if you over push the outer pose. Easy enough to readjust and often good to pull back a notch anyway.