Why some dvds duplicate first scene in second pgc?

[Talayero]

Now and then I find some dvd film with this structure:

pgc1 contains the whole film
pgc2 contains the 5 first minutes or so of the film.

These 5 first minutes are exactly the same as the ones that are in pgc1. I wasn't able to find any difference, as for instance the title of the film written in different languages. So I don't understand it. It must have some explanation.

Thanks in advance