Fear not, citizens of the Kalos region: you can now visit not-Paris without fear of losing all your precious indentured fighting creatures. Nintendo has issued updates to Pokemon X and Pokemon Y that fix a rather ugly bug. It was corrupting games if you saved inside certain areas of Lumiose City.
You can find the update in the eShop. If you bought the game digitally or have the cart it in your system, simply entering the eShop will automatically prompt you to download the update. The official description notes: "This update fixes a bug related to resuming your game after saving game data in Lumiose City. It also improves the filtering feature within the Global Trade Station (GTS)." The notes point out that X and Y have separate updates, so if you bought them both, you'll need to download two patches instead of just one.