Rotating the painter with a pen width set to 1 products wrong rendering output (double line) even with graphicssystem raster

While drawing rotated by 45 deg rectangles in QGraphicsScene (test program main.cpp) we obtain shapes having different widths of their sides (snap1.jpg, snap2.jpg). Moreover, on Windows XP side width can depend on the relative position of one rectangle upon the other (snap2.jpg). Looks like line width of one rectangle depends upon the boundigng rectangle of the other. All this is true only for pen size 1. All other sizes (inluding 0) do not produce such an effect.