OK I've found a fix for this.

In the 'Poser.ini' file the second to last line reads:

MAT_WACROS_ON 1

change it to

MAT_WACROS_ON 0

and it turns off the 'smart' gamma behaviour.

 

EDIT: or maybe not - I need to figure out if the texture cache remembers the wrong gamma settings or not, or if the 'smart' gamma is hopelessly inconsistent.

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Windows 10 x64 Pro - Intel Xeon E5450 @ 3.00GHz (x2)

PoserPro 11 - Units: Metres

Adobe CC 2017