Cannot add new subproject when using QBS build system

When using QBS build system I cannot add a new sub-project to the existing one from the context menu.

Steps to reproduce:

1. File > New File or Project > Non-Qt Project > Plain C++ Project (Qbs build)
2. In the Edit tab's Projects pane right click on the newly created project
3. A context menu appears where: Add New..., Add Existing Files..., Add Existing Directory..., New Subproject..., Add Library... menu items are all bold and are not doing anything.

Expected results:
I should be able to add a new sub-project or I should not see that entry there if I'm not supposed to add a new sub-project.

Actual results:
New Subproject... context menu entry does nothing (It is not working either for a similar qmake project). I've noticed that this option is only available only if you create from beginning a "Subdirs project" from File > New File or Project > Other Project > Subdirs project. But this is only available for qmake projects.
I can however manually edit the qbs files to add subprojects.