As mentioned in the forum thread, workaround is to turn down logging of 'org.hibernate.engine.jdbc.internal.JdbcCoordinatorImpl' until upgrade to one of the mentioned versions is possible.
The warning message "WARN o.h.e.j.internal.JdbcCoordinatorImpl - HHH000386: ResultSet had no statement associated with it, but was not yet registered" is logged when saving an entity with a generated Id.
This message was sent by Atlassian JIRA (v6.1-OD-09-WN#6144-sha1:62dfc48)