It's only in the Japanese version so far, but a bug's a bug. UPDATE: North American copies will be affected too.
Japanese gamers who have had the GBA Pokémon games since their launch last year are just now starting to find a bug that is screwing with how the game works.
Apparently, the internal clocks in the cartridges are on the fritz, and they are affecting time-lapse and other time-sensitive events in the game. This bug only seems to pop up in copies of the games that have been out for a year, but it's nothing so serious that corrupts or erases saved games.
NCL is willing to fix the problem for free, of course. It's not known yet if this problem exists in the English versions of the game (since the game hasn't been out a year yet), so there shouldn't be too much to worry about until next March, a year after the game has been out over here.
Update: Game Informer Online has reported on this story with an official comment from Nintendo of America. The company confirms that this bug will also affect the North American version of the game at the one year anniversary of its release, which will be in March. NOA has not announced any sort of recall as in Japan, but there may be action taken in the spring.