It's been a while I don't use Poser's hair room, but recently I used it to create wet hair. Looks beautiful, so I moved on to style it using the styling tool on the hair room. Looks even better.

Now, I'm not sure at which point it started to happen (i think it was after I saved the scene and reopened it later), but when I render the scene, the hair is flying all over the screen! On the preview window it's fine, but if I mark "Show Populated" for the hair group, the hair is all over my preview window. Then, if I clear my custom style (by clicking Grow Hair Guides again), it solves the problem, but the custom style is gone. 

In summary, looks like that the custom styled hair is messing up at some point, prolly when I save it. And apparently the same is happening on custom morphs too now. It was working fine before I started messing with custom hair. I tried reproducing the problem by saving and reloading a scene, but it didn't happen. Maybe there's something else playing a part in it. But I'm sure saving it has a big part on the issue.

Well, has anyone else had any problem like this? Not sure if this can be part of the cause but just recently I quit using the 'Use external binary morph targets' setting under General Preferences, so I can use a morph delete Python script.

Re-run the simulation and see if it goes away.  Where the guides are may not have any relation to where interpolated hair ends up.  It also might be that old cached simulation data is not interpreted the same way when loaded with a later patch or Poser version.  Also, changing the geometry of any colliders in any way (e.g. dialing a morph or scaling a body part)  after running the dynamic sim may make the simulation data invalid.

Ah no, theres no dynamics simulation. It's all static, styled hair.

Okay, then I dunno what to tell you.  Does this happen with a brand new scene and new hair object, or only with saved ones?  I see from the first post it seems like this is only with saved scenes.

I've just reset my PC and killed every single task that can be killed off the task manager.
I'll try again now to reproduce the problem.

Well, here's the deal:

The figure is Apollo Max. I have 3 hair groups on the head: one for the front part of the hair, one for mid, one for back. That makes it easier to style the hairs. Groups don't overlap.

I can work with my hairs, then I can render, and I can style them... no problems. But when I save my scene and load it again, the front and mid hair groups bugs out. Some hair strands fly all over the scene if I "Show Populated" or render the scene. The back group never bugs out. I see no difference between the 3 hair groups other that the back group was created last.

Not sure whats happening.

Sounds like you need to contact SM support.  Do yourself a favor and make sure this happens with one of their figures too, or else they tend to not be very interested in helping you, even though this sounds pretty obviously not the figure's fault.

Alright... after further testings, here's the solution to my problem for future reference:

Hair Room / 3. Styling Controls / Vents per hair = 100 ... is very bad! Thats what was causing the issue. It will work fine when you do it, but it will bug when you save then load your scene again.

Oh lord yeah, 100 verts per guide is crazy and immense overkill.  Even for very long hair, unless you're trying to do something like a huge afro, 25 verts or something like that should be fine.

It is. But anyways... it shouldn't bug out like that. And also, it does look great until you save your scene and load it again, so its definitelly another Poser bug...

i think its just a memory issue.
IMO strand hair  is  the most taxing element  for  the Poser program....at least for me, using P7.

BTW  - when you  are  working in the hair room,
how often do  you clear  out your undo  cache?

I can crash  Poser  any  time i need to  by  growing too much  hair.

And if  I am  correct, and, since it is wet hair you want,  you  might try  keeping the number of hairs  relatively  low  in  the goups-  like  10 to  15  thousand,  and make the roots and tips  thicker.

so  true on the verts thing,  only  if you  want  clean  smooth curves  on long hairs  do you  need a lot of verts