run: 

yum --showduplicates list clamav-db

if you run:

yum list updates

what do you get?

 Can you run:

yum --noplugins --showduplicates list clamav-db

...I'm guessing that the latest clamav-db is being excluded, and that is hiding the real update.

It's definitely being excluded - you can see that in the first set of debug output. I thought I had fixed this problem before, though. However, it could be a new problem b/c of where the priority plugin is excluding the pkgs.

I am facing same(?) problem on my test system.

I have a package with versions from 1.0-1 to 1.0-4:
  1.0-1 and 1.0-3 in repo3 (priority 20)
  1.0-2 in repo1 (priority 10)
  1.0-4 in repo2 (priority 30)

A) yum doesn't let me to install yum-priorities-test-pkgD-1.0-1 from repo3:

# yum -y install yum-priorities-test-pkgD-1.0-1.noarch

Loaded plugins: priorities, product-id, refresh-packagekit, rhnplugin, subscription-manager
Updating Red Hat repositories.
This system is not registered with RHN.
RHN Satellite or RHN Classic support will be disabled.
8 packages excluded due to repository priority protections
Setting up Install Process
No package yum-priorities-test-pkgD-1.0-1.noarch available.
Error: Nothing to do

B) When I install the 1.0-1 version manually from the repo3, yum ignores the update 1.0-3 from the repo3 and prefers 1.0-2 udpate from repo1 (because of higher priority)

# yum --disablerepo=\* --enablerepo=yum-priorities-test-repo3 install yum-priorities-test-pkgD-1.0-1
...

# yum update yum-priorities-test-pkgD
Loaded plugins: priorities, product-id, refresh-packagekit, rhnplugin, subscription-manager
Updating Red Hat repositories.
This system is not registered with RHN.
RHN Satellite or RHN Classic support will be disabled.
8 packages excluded due to repository priority protections
Setting up Update Process
Resolving Dependencies
--> Running transaction check
---> Package yum-priorities-test-pkgD.noarch 0:1.0-1 will be updated
---> Package yum-priorities-test-pkgD.noarch 0:1.0-2 will be an update

I don't think this is the correct behavior. I think that priorities plugin should not allow to update package installed from higher priority repo with an update from a lower priority repo. But it should let me to update the package from the install repo (repo3) even if there is another (but older) update in the higher priority repo (repo1).

 From the documentation in the plugin:

# By default, this plugin excludes packages from lower priority repositories
# based on the package name. If you want to exclude packages based ony the
# package name and architecture, enable the 'only_samearch' bool:
#
# only_samearch=N
#
# You can add priorities to repositories, by adding the line:
#
# priority=N
#
# to the repository entry, where N is an integer number. The default
# priority for repositories is 99. The repositories with the lowest
# number have the highest priority.

...so what should be happening is that when you have all three repos. enabled yum will hide everything except 1.0-2.

FWIW, while "yum update" doesn't update anything PackageKit-yum-plugin notices the updated packages and suggests to install them.

Thank you. I have finally reproduced this bug. 
Interesting thing is that the update is failing just because the available update in epel (low priority) repo. It works for me when I disable it.

 So I've created:

http://repos.fedorapeople.org/repos/james/pri.repo

...and I've tried a bunch of stuff, but AFAICS everything is working. Given both you and a customer have hit it ... I'm guessing I'm missing something (maybe the repos. need to be in a certain order -- although I did try a few variants).

Created attachment 524144 [details]
repository setup files

Did some more tests... Bug appears only with check_obsoletes=1 in priorities.conf.
This is strange because I do not have any extra obsoletes defined in my test packages.

A have attached the archive with my repo setup. There are 3 repo directories, each contains spec files of packages that will be built and included in the directory.

1. install yum-plugin-priorities
2. echo -e '[main]\nenabled = 1' > /etc/yum/pluginconf.d/priorities.conf
3. extract the archive to /tmp/testrepo
4. # cp /tmp/testrepo/yum-priorities-test.repo /etc/yum.repos.d/
5. # yum -y install yum-priorities-test-pkgB-1.0-1
6. # yum list updates
now 1.0-2 update is listed
7. # echo 'check_obsoletes=1' >> /etc/yum/pluginconf.d/priorities.conf
8. # yum list updates
now 1.0-2 update is not listed
9. # yum --disablerepo=yum-priorities-test-repo2 list updates
now 1.0-2 update is listed again


yum-priorities-test-repo2 (lowest priority) contains just yum-priorities-test-pkgB-1.0-3 built using following spec file.

# cat yum-priorities-test-pkgB.spec
Summary: yum-priorities-test-pkgB Package
Name: yum-priorities-test-pkgB
Version: 1.0
Release: 3
Group: System Environment/Base
License: GPL
BuildArch: noarch
Provides: yum-priorities-test-pkgB

%description

This is a yum-priorities-test-pkgB test package created by make_dummy_package.sh script

%files

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHBA-2011-1703.html