(A) After sentence is pronounced, the judge should allow the defendant to withdraw his plea of guilty or nolo contendere whenever the defendant, upon a timely motion for withdrawal, proves that withdrawal is necessary to correct a manifest injustice. (B) In the absence of a showing that withdrawal is necessary to correct a manifest injustice, a defendant may not withdraw a plea of guilty or nolo contendere as a matter of right once sentence has been pronounced by the judge.