Redshift suddenly stop working

Hello and thanks a lot for your very simple but very usefull application.

Since 2 days, redshift refuse to work on one of my computer.
All seems good, redshift start from command line, verbose mode display correct values and shift color in real time as expected.
But screen color temp stay the same.

Is there any way to debug more precisely to locate where my problem could be ?

Thanks in advance =)

Config :
redshift 1.6-1
xserver-xorg-video-nouveau 1:0.0.16+git20110411+8378443-1+b1
linux-image-2.6.39-2-amd64 2.6.39-2