The Auto IK feature ignores rotation locks when all three axis' are locked.

Repro:
1. Open the attached blend file.
2. Note that all three axis' of the shoulder rotation are locked.
3. Note that all but one of the axis' of the forearm are locked.
4. Grab the hand (auto ik should already be turned on) and move it about.
5. Note that the shoulder rotates, despite the rotation lock.
6. Note that the forearm properly only rotated on the one axis, as it should.

There are rigging situations where you want to exclude bones from auto IK (like hidden mechanism bones), and currently there isn't a way to do this without compromising parent-child relationships that may be important for other reasons.