Difference between U and P?

[Arancaytar]

When I update my local (unmodified) copy from the CVS repository, some
files that are being updated are flagged as "U" and others as "P". A
bit of searching has revealed this explanation:

U: updated
P: the version on the server is newer and the local copy has been
updated

I'm not seeing any difference between those two (except maybe that "U"
may be shown also when committing a changed file to the repository).
Why would updating a locally unchanged copy display both of these
apparently interchangeably?

The excerpt below is from a Drupal installation checked out from CVS:

cvs update: Updating includes
P includes/batch.inc
U includes/database.mysql-common.inc
P includes/database.mysql.inc
P includes/database.mysqli.inc
P includes/database.pgsql.inc
P includes/file.inc


--
Aran