Try it the other way around.  That is apply IK FIRST then the pose.  When IK is off the hand is not moved rather the shoulder and elbow move the hand.  The problem is that the hand has a known location, and IK is trying to apply that location to the hand and the hand is no longer at that location because it was moved by the rest of the arm, so when IK is turned on the hand is trying to move to where it thinks it should be.

Poser 5, 6, 7, 8, Poser Pro 9 (2012), 10 (2014), 11, 12, 13