Staying a decision is different from overturning it. Staying a decision does not mean that the decision has no effect. For example a plaintiff might win a case and the defendant would have to pay money. The defendant then appeals. Often the decision might be stayed on the grounds that if the plaintiff is paid he, she or it will abscond with the money during the pendency of the appeal. The defendant will often be able to get a stay pending appeal if he, she, it posts a bond. I do agree upon reflection that the law was to an extent premature in that the Supreme Court has not ruled on the issue. However, there are in many states laws on the books that are unconstitutional that are placeholders in case the law becomes constitutional. For example several states have laws making abortion illegal in anticipation of Roe v. Wade being overturned. So it was not appropriate for the legislature to pass the law in anticipation of the California Supreme Court upholding the finding that the prior law is unconstitutional. Of course if the California Supreme Court held the other way then the referendum law would have precedence until another referendum was passed. As such Arnold Schwarzenegger's reasons for vetoing the law aren't valid. if the California Supreme Court holds the referendum unconstitutional then the new law is perfectly valid. If the Supreme Court holds the prior law constitutional then there is no reason to veto this law as it would have no effect.