I've done something strange to my drawing. Whenever I have my drawing face on, no perspective, I cannot see the line I'm drawing until I release the left mouse button. However, when I have it in an isometric view, everything works as normal, i.e left click attaches the start of a line to a point, which then draws in the mouse direction along the work plane until the button is released to complete the line. I cannot work out what I've done to produce this effect, and it's driving me mad. Suffice to say everything works fine on a new blank drawing.