So, I wanted to export a neat MMD PMX 'stage' freebie to OBJ+MTL to use in Poser...
https://www.deviantart.com/shyuugah/art/MMD-Stage-DL-Corridor-887050518

01: Unpack using eg free Bandizip with its local 'code page' set such 'Asian glyphs' do not turn into 'dipthong alphabet soup'.
02: Use free PMX Editor to rename all materials and texture calls to English. eg 材質1 becomes 'Material1', ランプ1 becomes 'light1'...
03: Export to OBJ+MTL. Here, the ~8MB PMX becomes ~22MB. Import to Poser, iterate scale to taste. Here ~2.5%

04: As Poser_11.3 does not reliably auto-extract 'Alpha Channel' from mapped textures, deploy free Irfan View or, for eg DDS, free XN View.
05: Hand-apply those Alpha Channel maps to 'Transparency', 'Emission' maps to Ambience and/or Cycles' 'Emission' node.

Uh, why are my scene's texture maps up-side down ?
Yeah, yeah, PMX is opposite-handed to OBJ, also I may have told the PMX to 'render both sides'...
No problem: Rather than run all the texture files through eg Irfan View, vertically flipping, I'll just tick the 'Mirror_V' box in each 'Color_Texture' node.
Uh ? That should have worked, but did not...
Plan_B: clear that tick-box, set V_Scale from 1.000 to -1.000.
How odd ! That did not work, either...

At that point, I went for a belated snack-meal. Returning, re-fuelled and re-caffeinated, I found that Poser had sorta 'caught up' and flipped the texture.

For the next hour or so, as I changed textures' V_Scale to -1.000, most worked instantly, some took a few seconds, some needed a minute or two...

No obvious pattern / correlation 
Any idea what's going on ? Or how to 'nudge' Poser to refresh ??

This Superfly, progressive, 96 pixel-sample render took ~15 hours on networked 'Box'. Still a tad fuzzy, so I re-ran with 256: Now on 93%...