I am not able to reproduce this. Using 5.1.0.Final, 5.1.1-SNAPSHOT, and 5.0.10-SNAPSHOT.

I get:

{{
create sequence hibernate_sequence start 1 increment 1
create table authors (id serial not null, primary key (id))
create table books (id serial not null, author serial, primary key (id))
alter table books add constraint FKnywe9o5g4i0s745ki4vng48wd foreign key (author) references authors
{{