I'm having the same problem as you do. I hope there's no problem with the hardware. I read something about defective BB's that we're sold in Asia. It includes BB overheating, battery draining and camera flash that won't work.
i do have that issue when i have taken a lo of pics in one turn. i have to turn off flash restart the phone then turn flash back on to get it up and running.
The latest leaked OS 6 for the 9700 solves the camera flash problem.
I also had a camera flash that was not working with the official OS6, I then installed the leaked OS6 and it worked!