Canvas render issues when size is smaller than 64x64

import QtQuick 2.6
import QtQuick.Window 2.2

Window {
    visible: true
    width: 32
    height: 32

    Canvas {
        anchors.fill: parent

        renderStrategy: Canvas.Cooperative
        renderTarget: Canvas.FramebufferObject

        onPaint: {
            var ctx = getContext("2d");
            ctx.fillRect(0, 0, width, height);
        }
    }
}