Yum 2.2 w/ HTTP proxy fails w/ error "Cannot find a valid baseurl for repo:"

Hi,

Recently "yum check-update" and "yum update" has started producing the
error "Cannot find a valid baseurl for repo: ...".  Googling suggests
that other occurrences have been caused by network connectivity errors
or miss configured yum repository locations.  I am convinced that in my
case it is yum 2.2's inability to successfully download files through a
HTTP proxy that is the problem.  To work around the problem I
reinstalled yum 2.1 and upgrade using "yum --exclude=yum update".

Has anybody else had the same experience?
Can anybody suggest how to debug the code?  Running "yum -d 9 ..."
doesn't add anything useful.

I have 2 FC3 installations which I update manually using "yum update"
regularly.  Both have to use a HTTP proxy (different ones) to access
the Internet and both have the same problem.

HTTP proxy setting:

  [root@bridge ~]# env | grep HTTP
  HTTP_PROXY=http://rockover:8080/

Here is yum 2.1 working:

  [root@bridge ~]# rpm -q yum
  yum-2.1.12-0.fc3

  [root@bridge ~]# yum update
  Setting up Update Process
  Setting up Repo:  base
  repomd.xml                100% |=========================| 1.1 kB    00:00
  Setting up Repo:  updates-released
  repomd.xml                100% |=========================|  951 B    00:00
  Reading repository metadata in from local files
  base      : ################################################## 2622/2622
  updates-re: ################################################## 742/742
  Resolving Dependencies
  --> Populating transaction set with selected packages. Please wait.
  ---> Package yum.noarch 0:2.2.0-0.fc3 set to be updated
  --> Running transaction check

  Dependencies Resolved
  Transaction Listing:
    Update: yum.noarch 0:2.2.0-0.fc3
  Is this ok [y/N]: y
  Downloading Packages:
  Running Transaction Test
  Finished Transaction Test
  Transaction Test Succeeded
  Running Transaction
  Updating: yum 100 % done 1/2
  Completing update for yum  - 2/2

  Updated: yum.noarch 0:2.2.0-0.fc3
  Complete!

And here is yum 2.2 failing:

  [root@bridge ~]# rpm -q yum
  yum-2.2.0-0.fc3

  [root@bridge ~]# yum update
  Setting up Update Process
  Setting up Repos
  base                      100% |=========================| 1.1 kB     00:00
  Cannot find a valid baseurl for repo: updates-released

Thanks for your attention,
Mike
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