The jaw was rather tricky. There are two bones that need to move together, and they do not have a common parent unto themselves. That made the mouth slightly trickier. I also could not seem to get the inner eyebrow to raise by itself.
It's because mouth muscles should be free to be moved without open the mouth.
The design of the new rigging is complex because, in order to be 100% compatible with any engine, it doesn't need translation of bones.
So even translations are obtained as combination or rotations, using a technique called "pantograph" see image below.
So the mouth was spitted in two parts: mouth muscle movements (that must be independent from the jaw) and jaw rotation.
This is a bit tricky indeed, but it's intended to be controlled by a "control bone", still to implement, that should add at the export time.
But, I must confess, I am not used to having the eyebrow bones connected sequentially. I assume this is for IK in Blender?
No. It's because the restriction of using only rotation. Only last bone is the deforming one. The others are just pantograph connectors.
See the image below.
Also, is there a good place to report issues we find with the facial rig version of Makehuman? Is that needed? I suspect it's changing pretty quickly, so user discovered bugs might already corrected.
It's always good to have feedback with quality reports. The rigging is practically completed (except the derivation of other skeletons from it, and the generation of control bones) so if you see something wrong it can be certainly a bug. In any case, the worst thing that can happen is that the issue is rejected. The place where to post is:
http://bugtracker.makehuman.org/projects/makehumanThank you.