XDocument: saving XML to file without BOM

Question

I'm generating an utf-8 XML file using XDocument.

XDocument xml_document = new XDocument(
                    new XDeclaration("1.0", "utf-8", null),
                    new XElement(ROOT_NAME,                    
                    new XAttribute("note", note)
                )
            );
...
xml_document.Save(@file_path);

The file is generated correctly and validated with an xsd file with success.

When I try to upload the XML file to an online service, the service says that my file is wrong at line 1; I have discovered that the problem is caused by the BOM on the first bytes of the file.

Do you know why the BOM is appended to the file and how can I save the file without it?

As stated in Byte order mark Wikipedia article:

While Unicode standard allows BOM in UTF-8 it does not require or recommend it. Byte order has no meaning in UTF-8 so a BOM only serves to identify a text stream or file as UTF-8 or that it was converted from another format that has a BOM

Is it an XDocument problem or should I contact the guys of the online service provider to ask for a parser upgrade?