Parent folder for groups within modules not documented

Consider a module with a nested group:

import qbs 1.0

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

The documentation for groups sais:

By default, matching files are only picked up directly from the parent directory, but you can tell Qbs to consider the whole directory tree.

If the group is defined in a product, the parent directory is automatically set to the location of the product qbs file. For groups within modules, the parent directory is still the same location which is unexpected. For source files in the module directory, one has to set prefix explicitly to path (above example) which is not documented and also smells incosistent.