[rosser]

A grandfather clause like this doesn't make a law "retroactive". It exempts people who would be subject to the law because of things that happened before its passage from its effects, when the specific behavior in question (say, e.g., filing your taxes after the law's passage, on income earned before that passage) is newly affected. It prevents "punishing" people for behavior that wasn't contrary to the law, when they engaged in it.

It is, therefore, the exact opposite of retroactive.

EDIT: phrasing.

[delinka]

I think you've misunderstood me. I've reworded to help. I did not intend to imply that I thought such a clause made the law retroactive. I'm saying that by default, laws should not be retroactive and that needing a clause to specifically prevent retroactivity is annoying as it specifies what should already be the default.