Cave's Xbox Live Arcade action game Nin-2 Jump has a bug where your save data will be corrupted under specific conditions. This apparently occurs if save and end the game after a clearing a stage where you unlocked an achievement.
The official Cave blog reveals today that work on a fix for the bug is complete. A patch is undergoing testing and will be released some time this month.
In the meanwhile, the blog suggests that after unlocking an achievement, you keep on playing and save at the next save chance. Yes, you have a reasonable excuse to tell someone that you "have" to keep on playing.