Our development team has confirmed the issue and found that it was not a bug.
When using the real-time drawing function, the screen you see currently is fixed to the background and captured.
You may understand better if you use non full-screen size.
We are pleased to inform you that the real-time drawing function is now improved!
Please install Bandicam 3.4.0 from https://www.bandicam.com/downloads/ and check its performance.