Is Section 12280 amended to add new elements to the assault rifle offence?

Defendant contends he was improperly convicted of possessing an assault rifle because section 12280 was amended after the date of his offense, but before the date of his trial, to add a new subdivision (e). He argues, first, the amendment applies retroactively to his case because its provisions favor the defendant; and second, the amendment added additional elements to the offense which the People failed to prove. We agree defendant is entitled to the benefit of subdivision (e)'s provisions (Tapia v. Superior Court (1991) 53 Cal.3d 282, 301, 279 Cal.Rptr. 592, 807 P.2d 434), but do not agree subdivision (e) added new elements to the offense that the prosecution was required to prove to secure a conviction. A reading of section [8 Cal.App.4th 396] 12280, subdivision (e), in context, convinces us the factual exceptions in subdivision (e) constitute affirmative defenses on which defendant has the burden of proof.