Csharp 为什么xslWriter不总是按照xslWriterSet中指定的格式格式化该文档

BACKGROUND
I get a lot of xml files that contain no newlines and to quickly format them I use the function below.

SCENARIO
When I run the tool the first time on a file that contains no newlines (and no insignificant whitespace) then it works as expected:

Convert("myfile.xml", "  ");

如果我对刚刚格式化的同一文件再次运行该工具以增加收件箱，则收件箱不会更改:

Convert("myfile.xml", "    ");

QUESTION
Why is the file not formatted the second time I run the function? How do I make sure the function always formats the file?

public static void Convert(string filename, string indent)
{
    var input_string = File.ReadAllText(filename, Encoding.UTF8);
    var settings = new XmlWriterSettings
    {
        NewLineHandling = NewLineHandling.Entitize,
        Indent = true,
        IndentChars = indent,
        NewLineChars = Environment.NewLine
    };
    var sb = new StringBuilder();
    using (var reader = XmlReader.Create(new StringReader(input_string)))
    using (var writer = XmlWriter.Create(sb, settings))
    {
        writer.WriteNode(reader, false);
        writer.Close();
    }
    File.Delete(filename);
    Encoding utf8 = new UTF8Encoding(encoderShouldEmitUTF8Identifier: false);
    File.WriteAllText(filename, sb.ToString(), utf8);
}

NOTE
If I modify the reader to ignore whitespace then the writer can format the output correctly:

XmlReader.Create(new StringReader(input_string),
                 new XmlReaderSettings { IgnoreWhitespace = true })

但我仍然想知道为什么当标签之间存在微不足道的空白时，作者未能格式化输出.