Yeah, i haven't experienced this at all, and i've saved in Luminose City quite a few times. Not sure weather it's a glitch that only occurs in pokemon Y or what the deal is. I posted this same topic on the X&Y thread, not knowing this thread was up, lol..

I first read about the glitch on a friends FB page, with something about Missingno being encountered (probably fake) in X version that knew Megahorn and was super effective against everything.