Structure template not working with children document type having mandatory metadata having default value

At least in some cases, having a document type with mandatory metadata (a directory one for instance), even if this metadata has a default value, an automatic creation of this document type through structure template mechanism leads to error.

Reproduction steps:

1. Create a folderish document type A
2. Create a document type B
3. Add to B a custom mandatory metadata of type directory
4. Define a default legit value for this metadata
5. Add a Structure Template for type A, which should automatically create a document B under it
6. Deploy on a Nuxeo, and try to create a document A. This raises an error visible in server.log

org.nuxeo.ecm.core.api.validation.DocumentValidationException: 3 constraint violation(s) thrown. First one is: 'Please select a Region/Country', call DocumentValidationException.getViolations() to get the others

Example stacktrace enclosed.