Can't get back hair to sync up with head movement

The usual reason for putting the rear hair in a separate group is if you want some of the hair in front of the body and some of the hair behind. The only way i know of is to have a separate rear hair group so the upper structure is Head (with frontal hair) then Body then RearHair (like this puppet has done). But other complexity comes in depending on whether you want arms in front of or behind the body or face etc.

One feature I would love is to be able to specify depth for layers instead of (only) using the order of layers. The you could push some hair to the front and some to the back, but it's all in the Head layer.

Personally, I'd put the hair inside the head layer, put in on the head background layer, not set it to independent, attach the fixed handle of every strand to pivot with the scalp, then attach the dangle handles in each of the strands.

Oh, I always set "Attach to" to "auto". I have never had luck with anything else. I never worked out what it is for. 

Try removing the independence ("+") from the Back Hair group layer. Then attach the hair strands to the Head layer (no need for a separate handle). Drag the origin of the hair strands to the head at appropriate positions so the pivot points look good.

With Back Hair independent, the rear hairs are trying to attack to the Back Hair layer, then Back Hair is trying to attach to the head/body. This could cause problems (especially if "Back Hair" is empty, meaning the hairs have nothing to attach to). I suspect if you remove independence from teh Back Hair group the problems will go away