I've been noticing an oddity ... I think specific to P6 ... which sounds parallel to your problem. When a figure is built with some parts inside an attached prop, P6 seems to ignore those inner parts. In my case, I had built an instrument cluster with a needle, lens, meter face, etc, and then attached it to a car. The cluster showed up as an attached prop in the resulting figure, but the needle was no longer movable; it was just a fixed part with no parameters. The tail part within a hair prop sounds similar to a needle within a meter.

My python page
My ShareCG freebies