QML Canvas wrong length of drawing lines

import QtQuick 2.0

Item {
    Canvas {
        id: canvas
        smooth: true
        width: 800; height: 600

        onPaint: {
            var ctx = canvas.getContext('2d');
            ctx.clearRect(0, 0, canvas.width, canvas.height);
            ctx.rotate(canvas.rotate);
            ctx.lineWidth = 5;
            ctx.strokeStyle = ctx.createPattern("red", Qt.SolidPattern);

            ctx.beginPath()
            ctx.moveTo(10, 10)
            ctx.lineTo(30, 10)
            ctx.stroke()

            ctx.beginPath()
            ctx.moveTo(10, 20)
            ctx.lineTo(30, 20)
            ctx.lineTo(20, 20) //goes back 10 horizontally, and the line will be resized
            ctx.stroke()

            ctx.restore()
        } //end of onPaint
    } //end of Canvas
}