loop conformance

I'm in a grumpy mood today, so I decided to take out my frustrations on the ANS for CL, or implementations thereof. Consider carefully what the following form should return:

(let ((v (make-array 10 :initial-contents '(0 1 2 3 4 5 6 7 8 9) :fill-pointer 5))) (loop for x across v when (eql x 2) do (incf (fill-pointer v)) collect x))

ACL and SBCL both return (0 1 2 3 4). Probably every other implementation does too. I believe the ANS requires the return to be (0 1 2 3 4 5), although the definition in *6.1.2.1.5 The for-as-across subclause* uses various undefined terminology. (We of X3J13 understood that the loop specification was not our best work.)