[Samba] Samba 3.0.37 license confusion

[Ronnie Zheng]

Hello Jeremy and samba maintainers,

I am using Samba 3.0.37 and I am confused about the license.
On one hand both the COPYING file in the 3.0.37 tarball and your
website indicates that version 3.0.37 is GPLv2.
http://news.samba.org/announcements/samba_gplv3/

On the other hand, in the 3.0.37 tarball, there are many files with
GPLv3 headers without any exception. For instance, several file in
source/client directory.

So my question is if it is released under GPLv2, why there are so many
GPLv3 license only files ?

regards,
Rong.