[CentOS] packages downgraded when going from 5.0 to 5.1

Hello,

I have a few packages where the latest updated version in 5.0 is greater than the current 5.1 version.

Here is the list: package, installed version (from 5.0 updates), available (in 5.1)

flac 1.1.2-28.el5_0.1 1.1.2-27

flac-devel 1.1.2-28.el5_0.1 1.1.2-27

hpijs 1.6.7-4.1.el5.3 1.6.7-4.1

libsane-hpaio 1.6.7-4.1.el5.3 1.6.7-4.1

thunderbird 1.5.0.12-5.el5.centos 1.5.0.12-3.el5.centos

I use mirrors.ircam.fr, and apt+synaptic but I don't think that's the reason (except perhaps for the hp stuff?)

Is something wrong on my side? If not, should I downgrade those packages to the 5.1 versions?

Thanks in advance

cheers, Nicolas