What is the effect of failing to object under section 654 of the California Criminal Code?

Section 654, subdivision (a), provides in pertinent part: "An act or omission that is punishable in different ways by different provisions of law shall be punished under the provision that provides for the longest potential term of imprisonment, but in no case shall the act or omission be punished under more than one provision." Ordinarily, a section 654 claim is not waived by failing to object below. "[T]he waiver doctrine does not apply to questions involving the applicability of section 654. Errors in the applicability of section 654 are corrected on appeal regardless of whether the point was raised by objection in the trial court or assigned as error on appeal." (People v. Perez (1979) 23 Cal.3d 545, 549-550, fn. 3, 153 Cal.Rptr. 40, 591 P.2d 63.) This is an exception to the general rule that only those claims properly raised and preserved by the parties are reviewable on appeal. This exception is not required by the language of section 654, but rather by case law holding that a court acts in excess of its jurisdiction and imposes an unauthorized sentence when it fails to stay execution of a sentence under section 654. (See People v. Scott (1994) 9 Cal.4th 331, 354, fn. 17, 36 Cal.Rptr.2d 627, 885 P.2d 1040.)