JPAContainer - Hibernate vs EclipseLink

The Book of Vaadin and the Docs for JPAContainer recommends EclipseLink over Hibernate because EclipseLink is good at keeping connections for longer than Hibernate, and if Hibernate is to used then the entityManager-per-request pattern must be used (which is very good AFAIK)

I have used hibernate for 2 big development proyects with vaadin and are running in production for quite some time now without any issues regarding jpacontainer or hibernate, but I still want to understand why EclipseLink is recomended over Hibernate?

Can anyone provide some explanaition of why EclipseLink is recommended and what are the architectual diferences of both that where considered while making that advice?