The fact that this was in the South China Sea makes me wonder if the reason it's uncharted is that the Chinese recently created it; for some time they have been building artificial islands in the South China Sea in order to claim that entire body of water as Chinese territorial waters. (It's outrageous that this doesn't get a lot more international attention; it's as if the United States started building artificial islands around the boundary of the Gulf of Mexico in order to declare all of that to be US territorial waters. Imagine the outcry.)