I have switched from hibernate.hbm2ddl.auto=update to hibernate.hbm2ddl.auto=validate and hibernate is blaming that the sequence doesn't exist (even if Hibernate created it on the previous run):

Caused by: org.hibernate.HibernateException: Missing sequence or table: "cloudesire_sequence"
at org.hibernate.cfg.Configuration.validateSchema(Configuration.java:1295)

After setting a breakpoint, I see that Hibernate correctly retrieve the existing generator but its name contains double quotes (key = "hibernate_sequence").