Okay, now we are in the somewhat silly state of having 18000+ same-sex married couples, but no other same-sex couples are allowed to marry. But if California state law and government agencies are required to recognise those 18000+ couples as married, what about a same-sex couple married in another state?

Since the Court has interpreted Prop 8 as not invalidating those 18000+ legal marriages, I think the same interpretation requires recognition of same-sex marriages performed in states where it is still (or newly) legal. So there will be a loophole a mile wide!

The Prop 8 supporters have effectively lost.