Inheritance property failed, Qbs1.6.x works fine

import qbs

Project {
    name: "testqbs"
    minimumQbsVersion: "1.7.1"

    CppProgram {
        name: "qtcreatorcdbext"
        targetName: name

        files: [
            "main.cpp",
        ]

        installDir: {
            var dirName = name; // !!!!!!!!!!!!$%$#$@# change to 'parent.name' works well
            if (qbs.architecture.contains("x86_64"))
                dirName += "64";
            else
                dirName += "32";
            return dirName;
        }

        Group {
            fileTagsFilter: product.type
            qbs.installDir: installDir
            qbs.install: true
        }
    }
}