NLA Armature

Hello,
I have been expirimenting with animation, armatures, and ik solvers. However, i have several armatures, and all but one, when i add an IPO, shows up in the NLA editor. They only difference i can see is the ones that work, the ipo line is blue, where the one that doesnt work is yellow. They are all seperate objects, with 1 bone.

What different?