Unorthodox pick off move balk or not

Question
Can a right hand pitcher raise his left leg,as to pick a runner off third, but instead of throwing to third, bring his left leg back under in the same plane stepping towards first and execute the pick off to first. An umpire called this a balk, his reasoning being once the pitcher raised his left leg this was a motion to the plate. If this is true then why is it not a balk when a right had pitcher raises his leg and throws to third on a pick off, also to second base, when a pitcher raises his left leg and pivots  back towards second base on a pick off attempt. Also I have found nothing in the Major  League  Rules that states a pitcher must break contact with the pitching rubber on a pick off attempt, only that they step towards the base to which they are throwing.

Answer
Tim,

Balks are somewhat in the eye of the beholder.  I can't answer this question unless I would see the move and then can make a judgement.

If the umpire believes the pitcher is beginning his delivery to the plate, then the pitcher must deliver to the plate; otherwise it is a balk.

It is such a judgement call on this.

Brian