WYSIWYG editor strips part of code macro content

Steps to reproduce :

• Start with a vanilla instance of XWiki 15.10.5
• Create a new page, edit it in WYSIWYG mode, but do not use inline editing
• Add a code macro with the following content :

   cat > /var/www/html/info.php <<EOF
     <?php
        phpinfo();
     ?> 
   EOF

Expected :

When clicking "Submit" in the macro UI, you should see the code above being properly rendered in the editor.

Actual :

A code macro is inserted, but with the following content :

   cat > /var/www/html/info.php <<EOF
      
   EOF

Note : I initially thought that this issue could be fixed by XWIKI-21803, however I reproduced with the latest snapshot of 15.10.6.