Unexpected results with BLPattern about blend2d HOT 3 CLOSED

#include <blend2d.h>

BLImage render(const BLContextCreateInfo& cci) {
  BLImage imgPattern(300, 300, BL_FORMAT_PRGB32);
  double w = imgPattern.width();
  double h = imgPattern.height();
  double xc = w/2.0;
  double yc = h/2.0;

  {
	  BLContext ctxS(imgPattern);
	  ctxS.fillAll(BLRgba32(0xFFff0000));
	  ctxS.fillCircle(xc,yc ,0.21*w,  BLRgba32(0xFF0000ff));
	  ctxS.fillCircle(xc,yc, 0.11*w,  BLRgba32(0xFF888888));
	  ctxS.strokeLine(0,0,w,h,  BLRgba32(0xFFffff00));
	  ctxS.strokeLine(0,h,w,0,  BLRgba32(0xFFffffff));
	  ctxS.strokeLine(0,yc,w,yc,  BLRgba32(0xFFffffff));
	  ctxS.strokeLine(xc,0,xc,h,  BLRgba32(0xFFffffff));
	  ctxS.end();
  }

   // create the main BLContext
  BLImage img(400, 400, BL_FORMAT_PRGB32);
  BLContext ctx(img);
  ctx.clearAll();

  ctx.setTransform( {1,0,0,1, 200,200} ); //put the origin at the center of img

  BLPattern myPattern;
  myPattern.setImage(imgPattern);
    // put the origin of the pattern in its center
  myPattern.setTransform({1,0,0,1, xc, yc});

  // experimental variations :
  // myPattern.setTransform({1,0,0,1, xc+0.01, yc});  // it works !
  // myPattern.setTransform({1,0,0,1, xc+0.001, yc}); // still wrong
  // myPattern.setExtendMode(BL_EXTEND_MODE_REFLECT); // it works !
  ctx.setFillStyle(myPattern);

  ctx.fillCircle(0,0,90);
  ctx.end();

  return img;
}