i'm trying to rig a wing: i place my bones but when i add an IK from a target bone to the wing limbs (the "fingers" betwee...

i'm trying to rig a wing: i place my bones but when i add an IK from a target bone to the wing limbs (the "fingers" between the membranes), one set is jumping badly out of place - is there a reason for this, and how do i correct it? all the fingers are extruded so all the rolls match etc.