Steps to reproduce :

1. Create the file to override a content type : WEB-INF/param/content-types/org.ametys.web.default.Content.article.xml
2. Add your own global validator in it :

   <?xml version="1.0" encoding="UTF-8"?>
   <cms:content-type xmlns:cms="http://www.ametys.org/schema/cms">
       <cms:global-validators>
           <cms:global-validator class="my.own.GlobalValidator"/>
       </cms:global-validators>
   </cms:content-type>

3. Add a breakpoint into your validator in the method #validate(Content, Form, MetadataSet, Errors)
4. Restart your CMS
5. Edit a content (of the modified content type)
6. Nothing happens while saving