The problem: when the teacher writes on the Promethean Board with the pen, random lines will shoot out from where the pen touches the board, making it look like a line has been drawn.
The fix: Turn off the button (green light) on the side of the board. Unplug the board from the wall. Wait 3-5 minutes. Restart the computer. Plug the board back in. Push the button on the side of the board back on. Recalibrate.