Validation fails when xi:include elements are mixed with directly incldued ones

I have docbook xml content that uses xi:include elements. Validation finds the following correct (which is the expected behavior):

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN" "http://www.docbook.org/xml/4.4/docbookx.dtd" [
    <!ENTITY % xinclude SYSTEM "http://www.docbook.org/xml/4.4/xinclude.mod">
    %xinclude;
]>

<chapter id="chapterCloud">
    <title>Enabling stuff</title>
        <para>This chapter describes the deployment process. </para>
    <xi:include href="deploy_database.xml"
        xmlns:xi="http://www.w3.org/2001/XInclude" />
    <xi:include href="add_new_customer.xml"
        xmlns:xi="http://www.w3.org/2001/XInclude" />
</chapter>

However, the plugin considers the following invalid :

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN" "http://www.docbook.org/xml/4.4/docbookx.dtd" [
    <!ENTITY % xinclude SYSTEM "http://www.docbook.org/xml/4.4/xinclude.mod">
    %xinclude;
]>
<chapter id="chapterCloud">
    <title>Enabling stuff</title>
        <para>This chapter describes the deployment process. </para>
    <xi:include href="deploy_database.xml"
        xmlns:xi="http://www.w3.org/2001/XInclude" />
    <section><title>title</title>
        <para>dsd</para>
    </section>   
    <xi:include href="add_new_customer.xml"
        xmlns:xi="http://www.w3.org/2001/XInclude" />
</chapter>

This content should also be considered valid, as the files referenced by the xi:include elements are also <section> elements.
P.s.: I realized that this is probably simply because xi:include functionality is not actually supported, so the second example is considered invalid because there is something between </section> and </chapter>. So maybe this is the same issue/feature request as in
https://github.com/redhat-developer/vscode-xml/issues/175.

Start by reading the related issue #175 and the validation behavior for DocBook xi:include elements. Reproduce both XML examples and compare validation results, especially when direct content is mixed with included sections. Done means the second example is accepted when the referenced files contain section elements.