Rounded Rectangle outline lacks anti-aliasing

In Qt Quick 2.0 rounded rectangle borders are no longer properly anti-aliased (see the attached screenshot and example code below), which in most cases makes them unsuitable for professional UI designs. Current work-around is to define rounded rectangles using a BorderImage element. The lack of anti-aliasing is regression from QtQuick 1.x.

import QtQuick 2.0

Rectangle {
    width: 150; height: 150
    Rectangle {
        color: "black"
        width: 100; height: 100
        radius: 20
        anchors.centerIn: parent
    }
}