This is a display only issue, related to anti-aliasing 'enhancements' introduced from From Draw 10 onwards.

Change the view from Enhanced to normal and there will be no white line.

I hope that it is possible to alter the engine at some point to provide exceptions to touching straight line shapes. However this may add a speed penalty.

Until then if creating images for the web, you may have to overlap one of the shapes slightly and move it behind the previously touching shape.

FWIW this anti-aliasing issue is not exclusive to Draw.

HTH

Peter