Access Denied calling createSchemaBasedXML

I have a procedure created as AUTHID CURRENT_USER that can successfully call createSchemaBasedXML and schemaValidate on an XMLTYPE, but the same procedure changed to AUTHID DEFINER gets an "ORA-31050: Access denied" error.  The schema that owns the procedure has the XDBADMIN role, execute privileges on DBMS_XDB, and was the schema that registered the XSD file.  An ACL is set as follows:
        <acl description="All privileges to my user."
           xmlns="http://xmlns.oracle.com/xdb/acl.xsd"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="http://xmlns.oracle.com/xdb/acl.xsd
           http://xmlns.oracle.com/xdb/acl.xsd