nuxeo-platform-renderer FreeMarker templates behave differently between 9.10 and 10.1

The FreeMarker templates appear to work differently between 9.10 and 10.1. Document properties are dereferenced differently.

The following works in 9.10, but is broken in 10.1:

${form.dublincore.created.time?datetime?string.iso}

The following works in 10.1, but is broken in 9.10:

${form.dublincore.created?datetime?string.iso}

To reproduce, change the pom.xml:parent/version to one of 9.10 or 10.1 in the project:
https://github.com/dbnuxeo/nuxeo-orbeon
And modify nuxeo-orbeon-rest/src/main/resources/skin/obsearch2.ftl with one of the above examples to reproduce success/failure with mvn test