XML validation succeeds but should fail

I'm using XML serialization with XmlSerializer. Before I read a document I try to validate it against XSD to determine the correct version to select.

The validation succeeds - but should fail!

My validation code is:

var schemaSet = new XmlSchemaSet();
schemaSet.Add(null, XmlReader.Create(new StringReader(xsd)));

var document = XDocument.Load(new StringReader(xml));

var hasErrors = false;
document.Validate(schemaSet, (s, e) => hasErrors = true);

Console.WriteLine("Document has erros: {0}", hasErrors);
if (hasErrors == false)
    Console.WriteLine("!!!! THIS DOCUMENT IS VALID !!!!");

Output is:

Document has erros: False
!!!! THIS DOCUMENT IS VALID !!!!

DEMO

Also the code suggested by MSDN will validate successfully (also included in DEMO - commented out):

var settings = new XmlReaderSettings();
settings.Schemas.Add(null, XmlReader.Create(new StringReader(xsd)));
settings.ValidationType = ValidationType.Schema;
settings.ValidationFlags = XmlSchemaValidationFlags.ReportValidationWarnings;
settings.Schemas.Compile();

var contentReader = XmlReader.Create(new StringReader(xml), settings);
var document = new XmlDocument();
document.Load(contentReader);

var hasErrors = false;
document.Validate((s, e) => hasErrors = true);
Console.WriteLine("Document has erros: {0}", hasErrors);
if (hasErrors == false)
    Console.WriteLine("!!!! THIS DOCUMENT IS VALID !!!!");

The XSD for testing was stripped down to only one type containing only one property:

<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema
    targetNamespace="http://www.xxx.de/V1_1/LightningChartConfiguration"
    elementFormDefault="qualified" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="http://www.xxx.de/V1_1/LightningChartConfiguration" xmlns:tns="http://www.xxx.de/V1/Common" xmlns:pref="http://www.xxx.de/V1/Triggers">

    <xsd:element name="root" type="LightningChartConfigurationRoot_1_1"></xsd:element>

    <xsd:complexType name="LightningChartConfigurationRoot_1_1">
        <xsd:sequence>
            <xsd:element name="Version" maxOccurs="1" minOccurs="1">
                <xsd:simpleType>
                    <xsd:restriction base="xsd:string">
                        <xsd:enumeration value="V1_1"></xsd:enumeration>
                    </xsd:restriction>
                </xsd:simpleType>
            </xsd:element>
        </xsd:sequence>
    </xsd:complexType>
</xsd:schema>

The XML to test is:

<?xml version="1.0" encoding="utf-8"?>
<root xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xxx.de/LightningChartConfiguration">
  <Version>V1_0</Version>
  <LastChanged>2020-09-11T05:38:07.333359Z</LastChanged>
  <Data>
    <Discriminator>{DCA61812-A355-4709-A252-AC20EF7AE3E1}</Discriminator>
    <Nodes>
      <Node xsi:type="NodeChart_1_0">
        <NodeId>365325c7-6cbd-4e29-af16-b044ee2a141f</NodeId>
        <ImageIndex>3</ImageIndex>
        <DisplayName>Chart</DisplayName>
        <ValueType>DateTime</ValueType>
        <TimeDisplayType>Absolute</TimeDisplayType>
        <XAxisLabelsTimeFormat>HH:mm:ss:fff</XAxisLabelsTimeFormat>
        <XAxisRange>10</XAxisRange>
        <Trigger>
          <IsActive xmlns="http://www.xxx.de/V1/Triggers">false</IsActive>
          <StartingMode xmlns="http://www.xxx.de/V1/Triggers">Undefined</StartingMode>
          <StoppingMode xmlns="http://www.xxx.de/V1/Triggers">Undefined</StoppingMode>
          <Items xmlns="http://www.xxx.de/V1/Triggers" />
        </Trigger>
        <XAxisTitleVisible>true</XAxisTitleVisible>
        <RefreshRate>15</RefreshRate>
        <LegendBoxVisible>true</LegendBoxVisible>
        <LegendBoxPosition>9</LegendBoxPosition>
      </Node>
      <Node xsi:type="NodeYAxis_1_0">
        <NodeId>8af383f1-bf1a-4b1f-8cb4-bb2ee33a53be</NodeId>
        <ImageIndex>4</ImageIndex>
        <Parent>365325c7-6cbd-4e29-af16-b044ee2a141f</Parent>
        <DisplayName>Y-Achse</DisplayName>
        <AutoRange>true</AutoRange>
        <From>0</From>
        <To>10</To>
        <Color>#FF008000</Color>
        <ShowGridLines>false</ShowGridLines>
        <YAxisTitleVisible>true</YAxisTitleVisible>
      </Node>
      <Node xsi:type="NodeSeries_1_0">
        <NodeId>9f92503e-1cd7-4120-9602-0da6394db17a</NodeId>
        <ImageIndex>1</ImageIndex>
        <Parent>8af383f1-bf1a-4b1f-8cb4-bb2ee33a53be</Parent>
        <DisplayName>Testing XXXXXX</DisplayName>
        <Color>#FF00FF7F</Color>
        <Width>1</Width>
        <Pattern>Solid</Pattern>
        <Scale>1</Scale>
        <ShowInLegendBox>true</ShowInLegendBox>
        <PhysicalDimension>NoDimension</PhysicalDimension>
        <PhysicalUnit>NoUnit</PhysicalUnit>
        <Data>Testing</Data>
      </Node>
    </Nodes>
  </Data>
</root>

The XML is obviously much too large and contains a lot more tags as allowed by XSD. Nevertheless the XSD-Validation succeeds without any errors. The only tag allowed in XSD is version that has a restriction to V1_1 wheras in XML it is V1_0.

I created a DEMO that reproduces this wired behaviour.

What am I missing here? What do I need to do to make the XSD validation work as expected?

If you copy the XSD and XML to e.g. this page the validation will fail as expected.