clippingnode and drawdot bug?

hi i am using clipping node (3.0 alpha1) and drawdot to reveal a circular hole in a image. it works fine when i use drawPolygon. however when i use the drawDot the unmasked part is a square and not a circle. any ideas why this is so?

my code is something like this (modified in the default project)

DrawNode *stencil = DrawNode::create();
stencil~~>drawDot, 30, Color4F::GREEN);
ClippingNode *clipper = ClippingNode::create;
clipper~~>setPosition(Point(visibleSize.width/2 + origin.x, visibleSize.height/2 + origin.y));
addChild(clipper);

// add “HelloWorld” splash screen"
auto sprite = Sprite::create(“HelloWorld.png”);
clipper->addChild(sprite);