There was a post about it here. I'd like to clarify this issue.
I looked up the source code of OracleDataProvider class. There is method GetTableSchema that generates a metadata for each table. Actually, there no code related to any relations of the table! It just load columns and indexes. If you compare this method with corresponding one in SqlDataProvider you'll see there is a code loading foreign keys and many-to-many relations.
Could someone fix it or tell me what I've missed?