LUTs in region render clipping

[Simon van de Lagemaat]

Trying to get a show lut going in the region render and we're getting
consistent clipping in the highlights no matter what type of lut (csp and
cube) we try and no amount of preconditioning is helping... is this just a
case of the region render not being fp?  Is there a possible fix for this
I'm not aware of?