schema.xml & xi:include -> copyField source :'_my_title' is not a glob and doesn't match any explicit field or dynamicField

[Clemens Wyss DEV]

Given the following schema.xml
<?xml version="1.0" encoding="UTF-8" ?>
<schema name="locale_de" version="1.5">
  <uniqueKey>_my_id</uniqueKey>
  <field indexed="true" name="_version_" stored="true" type="long"/>
  <copyField dest="_my_suggest" source="_my_title"/>
  <fields>
    <field indexed="true" multiValued="false" name="_my_id" required="true" 
stored="true" type="string"/>
    <field indexed="true" multiValued="false" name="_my_title" required="true"  
stored="true" type="string"/>
    <field indexed="true" multiValued="true" name="_my_suggest" stored="false" 
type="string"/> 
  </fields>
   <types>
    <fieldType class="solr.StrField" name="string" sortMissingLast="true"/>
     <fieldType class="solr.TrieLongField" name="long" positionIncrementGap="0" 
precisionStep="0"/>
  </types>
</schema>

When I try to include the very schema from another schema file, e.g.:
<?xml version="1.0" encoding="UTF-8" ?>
<schema name="locale_de" version="1.5">
  <xi:include href="schema-common.xml" 
xmlns:xi="http://www.w3.org/2001/XInclude"/> 
</schema>

I get SolrException
copyField source :'_my_title' is not a glob and doesn't match any explicit 
field or dynamicField

Am I facing a bug or a feature?

Thanks
- Clemens