Common misconception

Although in the posed hypothetical, and in many practical cases, we're considering someone who both frobozzes and reproduces the covered work. Since the latter is a reserved right we must look to see if a license existed, and presuming the offered license was conditional on non-frobozification we would conclude that someone who frobozzes has no such license and can not legally practice any of the rights reserved to the copyright holder. Perhaps they have no interest in those activities, but that is not usually the case.

People who spread the belief that if frobozzing is not an aspect of copyright law that a copyright license can't be conditional on it are spreading misinformation.