[CentOS] Dependency problems

Hi folks,

I use mock quite extensively to build RPM packages for CentOS
(actually I use the plague build system, which in turn uses mock). I
have a mirror of the whole CentOS tree (on mirrors.ircam.fr, which
syncs directly from msync.centos.org), which my mock configs uses
exclusively.

When populating the mock chroot, I consistently get these errors for
packages in updates (and not in the base tree):

--> Running transaction check
--> Processing Dependency: freetype = 2.2.1-16.el5 for package: freetype-devel
--> Finished Dependency Resolution
Error: Missing Dependency: freetype = 2.2.1-16.el5 is needed by package freetype-devel
Cleaning up...

Of course, both freetype and freetype-devel (in this instance, but I
get the same error with other packages) are on the mirror server, and
both are the same version. The problem goes away if I rebuild the
repository metadata locally:

createrepo /var/ftp/pub/CentOS/5/updates/x86_64
createrepo /var/ftp/pub/CentOS/5/updates/i386

I cannot really say how different my local metadata are from upstream;
diff outputs so much data it is quite useless with this kind of files.

So I guess the metadata are incomplete in some way on the master
server, as I don't usually modify them in any way on my server; can
anyone confirm this or tell me what I am doing wrong?

I can supply the whole mock config files and the command used for
populating the mirror server if needed.

-- 
Arnaud