We're sure millions of 3DS owners are currently merrily playing Pokémon X or Y — or both if they're really keen — but some seem to be running into issues. It's being widely reported that some European and Japanese owners are running into a bug that corrupts their save and, unfortunately, prompts them to restart the game from scratch.
In these cases saving in Lumiose City prompts the save file to become unusable, with attempts to load the data simply bringing frozen screens — top and bottom — though the music continues to play. There doesn't seem to be a fix, and no information has been issued — at the time of writing — by Nintendo.
This seems to be affecting a small minority of copies, but it may be wise to avoid saving in Lumiose City for the time being. There are some videos showing this bug in action in Y, though that uploaded by a British gentleman is riddled with naughty words — and we can't have that — so you can check out a video from a Japanese user below; in that case we only have some unsavoury and excessive sniffing going on, though whether the gamer is swearing in Japanese is unknown. Oh YouTube, stay classy.