Crash on anchors : verticalCenter+left

import QtQuick 2.0

    Rectangle {
        id: g_firstForm
        x: 0
        y: 0
        height:500
        width:500
        opacity: 1

        Rectangle {
            id: g_backForm
            anchors.verticalCenter: parent.verticalCenter
            anchors.left: parent
            anchors.leftMargin: 27
            opacity: 1
        }

        Text {
            id: g_clue
            text: "Clue"
            anchors.verticalCenter: parent.verticalCenter
            anchors.horizontalCenter: parent.horizontalCenter
            font.pixelSize: 30
            font.family: "Arial-BoldMT"
            font.bold: true
            smooth: true
            x: 238
            y: 12
            opacity: 1
        }
    }