With IK chains and constraints, the IK target bone cannot be parented to any bone that is affected by the IK constraint. (This is what is causing the “flip out”.) For a typical human rig, the foot IK targets should be parented to the root or main bone of the rig. The hand IK targets often are parented to the chest or spine bones. In more advanced rigs, parent switches are used so the animator can choose if the hands follow the chest or the root bones.