I would still say given your answer that this rule is redundant because the rules are clearly set out for permanent residents, and you say that rule does not apply post-citizenship.
The next question I have deals with a person having dual citizenship. The law puts the onus of proof on the individual. That is very difficult to prove sometimes. It could lead to abuse. Why do you not put the onus of proof on the government to prove the person is a dual citizen, rather than the other way around?