When recording audio, your voice from the microphone is recorded separately to the other person’s voice, which comes from the PC audio.
FlashBack simply records what you see on your screen.
FlashBack simply records your desktop. When you lock your PC, your desktop is suspended so there is nothing for FlashBack to record.
Sometimes these are made from something called ‘layered windows’. By default, FlashBack does not record these because doing so can cause some performance issue.