It's only allowed if a government that does have the power creates new legislation to retrospectively authorise the tax. They've done it in the past when the tax that was ruled invalid had been in place for a long time, many people had made a lot of decisions based on it being valid, and unwinding it would have been highly disruptive. In this case, I don't think that applies - it hasn't been in place long and hasn't affected many people, so I would guess the Federal Government won't retrospectively authorise it and Victoria will end up refunding the money collected.
With a 4-3 High Court decision on its legality, I don't think anyone here acted in bad faith and a reprimand isn't warranted. You're essentially asking them to know Constitutional Law better than 3 High Court justices. They'll be paying the court costs for the plaintiffs and having to figure out how to unwind and refund the tax - that seems like punishment enough.