yum+preupgrade+anaconda: Cannot upgrade release with 'exclude=' entries in /etc/yum.conf

I've been trying to upgrade some of our systems using preupgrade, which 
uses a combination of yum + anaconda.  On our systems without any 
exclusions in /etc/yum.conf or /etc/yum/pluginconf.d/versionlock.list 
this all works fine, either by using 'preupgrade' or by doing a 'live 
upgrade' by installing the new release rpms and then doing a 'yum update 
--obsoletes'.  However, when we try to preupgrade a machine that has 
exclude entries in the yum config files then the release upgrade fails 
and we get a message like:

Error Message:
TurboGears-1.0.4.4-2.fc9.noarch.rpm cannot be opened.  This is due to a 
missing file, a corrupt package or corrupt media.


It turns out that TurboGears is one of the packages in the 'exclude=' 
list in /etc/yum.conf.   So it looks like there is a disconnect between 
the 'yum' part of the preupgrade processing and the 'anaconda' part of 
the process.

Is there some way to configure yum or anaconda such that we can do a 
preupgrade on systems having package exclusions in the yum config files?


Regards,
Gerry