The reason for the discrepancy in the generated DDL files appears to be a conflict between the hibernate definitions for HibernateStringInstance.hbm.xml, StringInstance.hbm.xml and (potentially) JcrNodeInstance.hbm.xml.

Each of these VariableInstance subclasses map entries onto the JBPM_VARIABLEINSTANCE using the same field, STRINGVALUE_, but only StringInstance.hbm.xml specifies the length. The length is obviously being ignored when the DDL files are created as the HIbernateStringInstance.hbm.xml is being loaded first.