XmlNode SelectNodes returns only first occurrence when querying for text nodes

Seeing strange behavior when querying for text nodes with the text() XPath function.

I have a simple XML like

<label>Matrise <foo/><foo/>GM:1<foo/></label>

Using labelNode.SelectNodes("text()") query will return the 2 expected text nodes - "Matrise" and "GM:1"

However, if I remove the foo nodes then there will still be two text nodes, but the query no longer returns both of them - only the first.

Why is it returning only one text node in the first case if there are clearly two text nodes?

Code example:

using System.Xml;

var xml = "<label>Matrise <foo/><foo/>GM:1<foo/></label>";
var doc = new XmlDocument();
doc.LoadXml(xml);
var labelNode = doc.SelectSingleNode("label");

Console.WriteLine("Before modifications:");
PrintTextNodesInOriginal(labelNode);

Console.WriteLine("\r\nAfter modifications:");
PrintTextNodesInModified(labelNode);


void PrintTextNodesInOriginal(XmlNode labelNode)
{
    PrintTextNodes(labelNode);
}

void PrintTextNodesInModified(XmlNode labelNode)
{
    // Remove foo nodes
    var foos = labelNode
        .SelectNodes("foo")
        .Cast<XmlNode>()
        .ToList();

    foreach (var foo in foos)
    {
        foo.ParentNode.RemoveChild(foo);
    }

    PrintTextNodes(labelNode);
}

List<XmlNode> GetTextNodes(XmlNode labelNode)
{
    return labelNode.SelectNodes("text()")
        .Cast<XmlNode>()
        .ToList();
}

void PrintTextNodes(XmlNode labelNode)
{
    var textNodes = GetTextNodes(labelNode);
    var textNodesActual = labelNode.ChildNodes
        .Cast<XmlNode>()
        .Where(node => node.NodeType == XmlNodeType.Text)
        .ToList();

    Console.WriteLine($"Nodes count using query: {textNodes.Count}");
    Console.WriteLine($"Nodes count actual: {textNodesActual.Count}");
    Console.WriteLine("Nodes' contents:");

    foreach (var textNode in textNodes)
    {
        Console.WriteLine(textNode.InnerText);
    }
}

Expected results:

Before modifications:
Nodes count using query: 2
Nodes count actual: 2
Nodes' contents:
Matrise
GM:1

After modifications:
Nodes count using query: 2
Nodes count actual: 2
Nodes' contents:
Matrise
GM:1

Actual results:

Before modifications:
Nodes count using query: 2
Nodes count actual: 2
Nodes' contents:
Matrise
GM:1

After modifications:
Nodes count using query: 1
Nodes count actual: 2
Nodes' contents:
Matrise

The XPath data model does not allow the children of an element node to contain two adjacent text nodes. So while an underlying tree model such as DOM might allow this, a correct XPath implementation will treat them as if they were merged into a single node. Some XPath implementations handle this incorrectly, but it looks as if this one gets it right.

The reason for the rule in XPath is that it tries to ensure that if two XDM trees have the same XML serialization, then they are equivalent in terms of any XPath query.