Maya Constraints

I created a reverse foot setup and constrained it to the ik chain and structure of the foot. Every works fine - the leg bends and the foot rolls like it's supposed to. However, after setting a keyframe in the animation the reverse foot is no long controlling the actual foot.

snvn, " after setting a keyframe in the animation the reverse foot is no long controlling the actual foot"

You have probably set a keyframe on the actual foot bone.
You should place keys only on controllers you created - in your case its probably the reverse foot or some other nulls controlling the reverse foot.