http://www.bbc.com/news/world-asia-30642354 EDIT: As things unfold speculation appears more. You are supposed to keep 10 miles from storms. The weather over Java sea that day was just storms all over the place, but there were various other planes not far away, but all higher.
BBC says, "source quoted by Reuters said that radar data appeared to show that the aircraft's "unbelievably" steep climb may have been beyond the Airbus A320's limits."
Here, Bruce Dickinson demonstrates what an A320 does when flying too slow and you suddenly go, or pull, upwards...
https://www.youtube.com/watch?v=IKBABNL-DDM All very worrying and somewhat concerning. What was the weather up to...