I -and others- have submitted bug reports for this.  The default of gamma:1 for a new node is fine;  it is *not* OK to reset image map gamma to 1 after I have specifically set it otherwise.

     The behavior isn't consistent.  Both of these image maps are similar in hue and brightness (Genetica makes them this way).  Both drive diffuse and bump.  Poser reset the gamma of one but not the other.  So, one appears noticeably brighter.

     Every.  Time.  I  Open.  The.  Scene.

Poser 12, in feet.  

OSes:  Win7Prox64, Win7Ultx64

Silo Pro 2.5.6 64bit, Vue Infinite 2014.7, Genetica 4.0 Studio, UV Mapper Pro, UV Layout Pro, PhotoImpact X3, GIF Animator 5