Does the plain error rule apply retroactively to a change in the criminal code?

Appellants argue that application of the plain error rule is inappropriate based upon the doctrine of retroactivity articulated in Ingber v. Enzor, 841 F.2d 450 (2d Cir.1988). In Ingber we applied substantive changes in well-settled rules of criminal law retroactively, notwithstanding that challenges to those rules were first made on appeal. Id. at 454. Appellants therefore argue that Ingber establishes an exception to the contemporaneous objection requirement where a substantive rule of criminal law has been changed.