you can´t orientConstrain an IK_node. well you actually can, but with unpredicted results. an IK_node is just for moving purpose. the IKnode is the endNode and kind of a control node of 3 joints. by moving the IK handle you have a backTrace going on from the last to the first joint, where the movement is computed in a reverse mode. probably wrong explanation, but this is how I understand the stuff. therefore it doesn´t make sense to apply IK to just 1 joint as you did.
if you want to orient the neckJoint the simpliest solution would be to just orientConstrain your neckJoint to a CTRL-object. no IK setup is needed. whenever you pick the CTRL then it roteates the neckjoint.
and forget about orienting IK handles. this is simply not possible and also not intended to be.
hope that helped.
everything starts and ends in the right place at the right time.