Attaching Module Properties to Groups within Modules is Undefined

Consider a module with a nested group:

import qbs 1.0

Module {
    Depends { name : "cpp" }
    Group {
        prefix: path + "/"
        files : [
            "file.cpp"
        ]
        cpp.optimization : "fast"
    }
}

It is not defined, if cpp module properties can be attached to a group within a module file. In fact, only properties of the product that loads the module are applied. cpp.optimization in the above example is ignored.
Moreover, it could be replaced by any string and would not throw an error. I would expect similar behaviour in both products and modules.