I have an iPhone 4S 32 GB model. It is not jailbroken, and I do not have any camera-specific apps installed.
Sometimes when I switch between front and rear cameras during a FaceTime session, upon switching back to the front camera the image that I am sending will either be flickering (occasional black frames) or it will be completely black. This is confirmed both by me as well as the viewer on the other end. Only by switching between cameras a second time can I get this problem to go away.
Is there a known bug/cause for this problem, or is it something I am doing wrong myself?