Bug in Json.NET 4.0r1?

gistfile1.cs

public void Test()
{
	var serializer = new Newtonsoft.Json.JsonSerializer();

	using (var memoryStream = new MemoryStream())
	{
		using (var bsonWriter = new BsonWriter(memoryStream))
			serializer.Serialize(bsonWriter, 12345);

		Console.Write("Stream length is: " + memoryStream.Length); // shouldn't be *0*!
	}
}