Hello dear Orbeon team.
I've placed this message also as github issue (sorry for that, that was before I've noticed this google groups).
I have noticed a bug or maybe this use case is handled different that I understand.
I have simple form (made also on orbeon demo, but replicates also on orbeon 2023) that has two simple sections each with 4 inputs.
Second second come from app/library.
Whenever I catch xxforms-value-changed event and try to modify form model based on that change it works as long as it is not inner section from library.
Confirmed with xforms-inspector, out fr-form-instance is updated whilst inner is not.
From what I understood by reading documentation
https://doc.orbeon.com/xforms/xbl/advanced-topics/extensions#xxbl-mirror-attributeit should work.
This is my currently published form that shows this error in action:
https://demo.orbeon.com/demo/fr/buh123/nah123/new?form-version=1
and here is the xml code for form generating this issue (notice 2 extra xxforms-value-changed listeners at the bottom working on from change on top left control and propagating value to the other three):
<xh:html xmlns:xh="http://www.w3.org/1999/xhtml" xmlns:xf="http://www.w3.org/2002/xforms"
     xmlns:xs="http://www.w3.org/2001/XMLSchema"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xmlns:ev="http://www.w3.org/2001/xml-events"
     xmlns:xi="http://www.w3.org/2001/XInclude"
     xmlns:xxi="http://orbeon.org/oxf/xml/xinclude"
     xmlns:xxf="http://orbeon.org/oxf/xml/xforms"
     xmlns:map="http://www.w3.org/2005/xpath-functions/map"
     xmlns:array="http://www.w3.org/2005/xpath-functions/array"
     xmlns:math="http://www.w3.org/2005/xpath-functions/math"
     xmlns:exf="http://www.exforms.org/exf/1-0"
     xmlns:fr="http://orbeon.org/oxf/xml/form-runner"
     xmlns:saxon="http://saxon.sf.net/"
     xmlns:sql="http://orbeon.org/oxf/xml/sql"
     xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"
     xmlns:fb="http://orbeon.org/oxf/xml/form-builder">
  <xh:head>
    <xf:model xxf:custom-mips="fr:persist" id="fr-form-model" xxf:expose-xpath-types="true"
         xxf:analysis.calculate="true">
      <!-- Main instance -->
      <xf:instance id="fr-form-instance" xxf:exclude-result-prefixes="#all" xxf:index="id">
        <form>
          <section-1>
            <grid-1>
              <control-1/>
              <control-2/>
              <control-3/>
              <control-4/>
            </grid-1>
          </section-1>
          <section-2>
            <grid-1 xmlns:xbl="http://www.w3.org/ns/xbl" xmlns:xxbl="http://orbeon.org/oxf/xml/xbl"
                xmlns:p="http://www.orbeon.com/oxf/pipeline"
                xmlns:frf="java:org.orbeon.oxf.fr.FormRunner"
                xmlns:fbf="java:org.orbeon.oxf.fb.FormBuilderXPathApi"
                xmlns:oxf="http://www.orbeon.com/oxf/processors"
                xmlns:component="http://orbeon.org/oxf/xml/form-builder/component/buh123/library">
              <contA/>
              <contB/>
              <contC/>
              <contD/>
            </grid-1>
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          </section-2>
        </form>
      </xf:instance>
      <!-- Bindings -->
      <xf:bind id="fr-form-binds" ref="instance('fr-form-instance')">
        <xf:bind id="section-1-bind" name="section-1" ref="section-1">
          <xf:bind id="grid-1-bind" ref="grid-1" name="grid-1">
            <xf:bind id="control-1-bind" ref="control-1" name="control-1" xxf:whitespace="trim"/>
            <xf:bind id="control-2-bind" ref="control-2" name="control-2" xxf:whitespace="trim"/>
            <xf:bind id="control-3-bind" ref="control-3" name="control-3" xxf:whitespace="trim"/>
            <xf:bind id="control-4-bind" ref="control-4" name="control-4" xxf:whitespace="trim"/>
          </xf:bind>
        </xf:bind>
        <xf:bind id="section-2-bind" ref="section-2" name="section-2"/>
      </xf:bind>
      <!-- Metadata -->
      <xf:instance id="fr-form-metadata" xxf:readonly="true" xxf:exclude-result-prefixes="#all">
        <metadata>
          <application-name>buh123</application-name>
          <form-name>nah123</form-name>
          <title xml:lang="en">testing</title>
          <description xml:lang="en"/>
          <grid-tab-order>default</grid-tab-order>
          <library-versions>
            <_>1</_>
            <orbeon>1</orbeon>
            <app>1</app>
          </library-versions>
          <created-with-version>2025.1.1.202604250538 PE</created-with-version>
          <updated-with-version>2025.1.1.202604250538 PE</updated-with-version>
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          <email>
            <templates>
              <template name="default">
                <headers/>
                <exclude-from-all-control-values/>
              </template>
            </templates>
            <parameters/>
          </email>
        </metadata>
      </xf:instance>
      <!-- Attachments -->
      <xf:instance id="fr-form-attachments" xxf:exclude-result-prefixes="#all">
        <attachments/>
      </xf:instance>
      <!-- All form resources -->
      <xf:instance xxf:readonly="true" id="fr-form-resources" xxf:exclude-result-prefixes="#all">
        <resources>
          <resource xml:lang="en">
            <control-1>
              <label/>
              <hint/>
            </control-1>
            <control-2>
              <label/>
              <hint/>
            </control-2>
            <control-3>
              <label/>
              <hint/>
            </control-3>
            <control-4>
              <label/>
              <hint/>
            </control-4>
            <section-1>
              <label/>
            </section-1>
            <section-2>
              <label>testing123</label>
              <help/>
            </section-2>
          </resource>
        </resources>
      </xf:instance>
    </xf:model>
  </xh:head>
  <xh:body>
    <fr:view>
      <fr:body xmlns:xbl="http://www.w3.org/ns/xbl" xmlns:p="http://www.orbeon.com/oxf/pipeline"
           xmlns:oxf="http://www.orbeon.com/oxf/processors">
        <fr:section id="section-1-section" bind="section-1-bind">
          <fr:grid id="grid-1-grid" bind="grid-1-bind">
            <fr:c y="1" x="1" w="6">
              <xf:input xmlns="http://orbeon.org/oxf/xml/form-builder" id="control-1-control"
                   bind="control-1-bind">
                <xf:label ref="$form-resources/control-1/label"/>
                <xf:hint ref="$form-resources/control-1/hint"/>
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                <xf:alert ref="$fr-resources/detail/labels/alert"/>
              </xf:input>
              </fr:c>
            <fr:c y="1" x="7" w="6">
              <xf:input xmlns="http://orbeon.org/oxf/xml/form-builder" id="control-2-control"
                   bind="control-2-bind">
                <xf:label ref="$form-resources/control-2/label"/>
                <xf:hint ref="$form-resources/control-2/hint"/>
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                <xf:alert ref="$fr-resources/detail/labels/alert"/>
              </xf:input>
            </fr:c>
            <fr:c x="1" y="2" w="6">
              <xf:input xmlns="http://orbeon.org/oxf/xml/form-builder" id="control-3-control"
                   bind="control-3-bind">
                <xf:label ref="$form-resources/control-3/label"/>
                <xf:hint ref="$form-resources/control-3/hint"/>
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                <xf:alert ref="$fr-resources/detail/labels/alert"/>
              </xf:input>
            </fr:c>
            <fr:c x="7" y="2" w="6">
              <xf:input xmlns="http://orbeon.org/oxf/xml/form-builder" id="control-4-control"
                   bind="control-4-bind">
                <xf:label ref="$form-resources/control-4/label"/>
                <xf:hint ref="$form-resources/control-4/hint"/>
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                <xf:alert ref="$fr-resources/detail/labels/alert"/>
              </xf:input>
            </fr:c>
          </fr:grid>
        </fr:section>
        <fr:section id="section-2-section" bind="section-2-bind">
          <xf:label ref="$form-resources/section-2/label"/>
          <component:section-1 xmlns:component="http://orbeon.org/oxf/xml/form-builder/component/buh123/library"
                     xmlns="http://orbeon.org/oxf/xml/form-builder"
                     xmlns:xxbl="http://orbeon.org/oxf/xml/xbl"
                     xmlns:fbf="java:org.orbeon.oxf.fb.FormBuilderXPathApi"
                     xmlns:frf="java:org.orbeon.oxf.fr.FormRunner"
                     id="section-2-content-control"/>
        </fr:section>
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        <xf:action ev:observer="fr-form-instance" event="xxforms-value-changed"
              if="event('node')/name()='control-1'">
          <xf:setvalue ref="xxf:instance('fr-form-instance')//control-2"
                 value="xxf:instance('fr-form-instance')//control-1"/>
          <xf:setvalue ref="xxf:instance('fr-form-instance')//control-3"
                 value="xxf:instance('fr-form-instance')//control-1"/>
          <xf:setvalue ref="xxf:instance('fr-form-instance')//control-4"
                 value="xxf:instance('fr-form-instance')//control-1"/>
        </xf:action>
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        <xf:action ev:observer="fr-form-instance" event="xxforms-value-changed"
              if="event('node')/name()='contA'">
          <xf:setvalue ref="xxf:instance('fr-form-instance')//contB"
                 value="xxf:instance('fr-form-instance')//contA"/>
          <xf:setvalue ref="xxf:instance('fr-form-instance')//contC"
                 value="xxf:instance('fr-form-instance')//contA"/>
          <xf:setvalue ref="xxf:instance('fr-form-instance')//contD"
                 value="xxf:instance('fr-form-instance')//contA"/>
        </xf:action>
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        <fr:xforms-inspector/>
      </fr:body>
    </fr:view>
  </xh:body>
</xh:html>