Documents with same Raven-Entity-Name not grouped into collection

Question

I've got this weird situtation with Ravendb collections.

Saved two documents with exactly the same metadata:

Documents:

{
    "Title": "Some title",
    "ProductType": "Some type",
    "Description": "Some description",
    "Keywords": "Some keywords"
}

Metadata:

{
    "Raven-Entity-Name": "MetaDatas",
    "Raven-Clr-Type": "DomainModel.MetaData, DomainModel"
}

The ravendb studio won't show them into one collection and loading/querying the documents via C# code gives me always null as result:

var metaData = Session.Query<MetaData>().SingleOrDefault(m => m.ProductType == productType);

and

var metaData = Session.Load<MetaData>("MetaDatas-1");