Regression in list concatenation

import QtQuick 2.0

Item {
    property variant list2

    Component.onCompleted: {
        list2 = ["1", "2"]
        // listObject.mylist is a QStringList property coming from C++
        // of size 2 ("hello","world")
        list2 = list2.concat(listObject.mylist)
        for (var i = 0; i < list2.length; ++i)
            console.log(list2[i])
    }
}