Setting readonly properties doesn't generate an error

Take a look at the attached project (qbs-example/qtquick-app/qtquick-app.qbs):

    Group {
        fileTagsFilter: ["application"]
        qbs.install: true
        qbs.installRoot: "~/HereIKeepAllMyBinaries"
    }

Setting qbs.installRoot doesn't have any effect and doesn't generate an error either. In conjunction with the fact that documentation does not say that qbs.installRoot is read-only (QBS-1063) it is very confusing.