The rule is that everything must matched and that can be enforced at any point from airport security to the airline to customs. However, the rule and reality differ...

It's not unheard of for last names to get put before the middle name on forms and I'm fairly sure I've seen airlines do this intentionally in the past, although not on a ticket. However it's still violates the rule which means you have to decide how much risk you want to take -- push for a change / reissue and lose a few bucks or take a gamble.