Kai-Uwe Behrmann has found a nasty bug in 2.1 on absolute colorimetric intent when display profiles are involved. :-( The issue is solved in GIT, but not in the 2.1 distribution. Too bad. Well, It is not so terrible because it only affects the combination of abs. colorimetric and display profiles, but anyway ...
The specs on ICC V4 are pretty messed out when regarding to absolute colorimetric intent. There is now something called "ICC absolute", which is same that relative on display profiles and preserves paper white on output profiles. Basically the observer is assumed to be fully adapted to whatever illuminant being used to create the profile, this has severe implications on monitor profiles, and no effect on printer profiles measured under D50. So right now we have the v2 absolute, wich says nothing about the observer adaptation state and v4 absolute which assumes full adaptation.
I tried to do my best in supporting all modes (v2 and v4) by implementing what the white paper below describes, a knob to adjust the degree of chromatic adaptation, a feature that may be useful for match-to-screen applications. See cmsSetAdaptationState() on the manuals.
Many thanks Kai-Uwe for catching the bug!