for all of you interested in this trick: it's actually a trick.
when you browse X, hfs loads the content from disk, but it will skip every file/folder that has the same name in the virtual file system.
so, if you create under X a virtual folder Y, totally unrelated to the C:\X\Y folder, you'll see only this virtual Y when browsing X.
this is a wanted behaviour, adding some flexibility to virtual folders.