Be sure that you've actually parented the hair to the figure's head and not for instance the dress or something else.

I've had hair that needed to be reloaded and re-parented before it would stick though.. so I'm not quitee sure what causes it. I've just shrugged and contributed it to "Poser's Quirks" :lol:

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You just can't put the words "Poserites" and "happy" in the same sentence - didn't you know that? LaurieA
  Using Poser since 2002. Currently at Version 11.1 - Win 10.