Some PoseBones ignore some of my IK limits and forces them to zero

Hi all,

I programmatically set the rotation limits of the bones of an armature.
Setting the limits as constraints works well.
I am trying to set the same values as limits for the IK.

However, for some of the bones, the ik_min_x/z is ignored.
Whether I set it via code or script, it is locked to 0.

I attach an example scene. By running the script you will see that the increment is ignored.
You can try also via GUI.

I wonder if it is a bug or it is some hard-to-predict behavior.
Why are the limits reset even before creating the IK chain?

Tested on Blender 2.76b and 2.77a


BonesRotationTest.blend (491 KB)