Paint.NET :: Line Tool Not Visible?

have just downloaded paint.net - no problem on many basic functions but cannot get the line tool to give me a visible line. I have changed primary and secondary colors to make sure regardless of whether I'm left or right clicking the line will stand out against white background. I have increased width to six pixels to make sure it will be nice and thick and visible. I do get the four little box thingies when I release the cursor, and I can then go in and manipulate them. But no matter what I try I cannot SEE a line.