"What mesh is that in the .jpg  ?"

3rd Gen DAZ mesh. Modified, of course, but nothing extraordinary.

Both figures are custom sculpted (DAZ morphs & ZBrush), re-rigged and one is weightmapped, the other not.

Must have something to do with normals, as it happens on the raw object file, too. I tried to smooth it out and do some other tricks I have, but it was persistant.

Doesn't happen on "vanilla" David 3 for example, but of course this is way beyond my tolerance threshold for "Poser Peculiarities".

Especially as there was no other performance improvement or flaw fix whatsoever for me. (Tested render speed several times)

Well, SR1 is supposed to fix standard V4's exploding butt, but I didn't bother checking after discovering this. If I really feel the insatiable need to use V4, I either use V4WM or one of my own custom V4s anyway.

:-(