WiX: Extracting Binary-string in Custom Action yields string like "???good data"

I just found a weird behavior when attempting to extract a string from the Binary table in the MSI.

I have a file containing Hello world, the data I get is ???Hello world. (Literary question mark.)

Is this as intended?
Will it always be exactly 3 characters in the beginning?

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Sample code:

[CustomAction]
public static ActionResult CustomAction2(Session session)
{
    View v = session.Database.OpenView("SELECT `Name`,`Data` FROM `Binary`");
    v.Execute();

    Record r = v.Fetch();
    int datalen = r.GetDataSize("Data");
    System.IO.Stream strm = r.GetStream("Data");
    byte[] rawData = new byte[datalen];
    int res = strm.Read(rawData, 0, datalen);
    strm.Close();

    String s = System.Text.Encoding.ASCII.GetString(rawData);
    // s == "???Hello World"

    return ActionResult.Success;
}

Wild guess, but if you created the file using Notepad, couldn't that just be your byte order mark?