bug?: gpg warnings during apt set (while upgrading squeeze -> wheezy)

[Itay <debian@itayf.fastmail.fm>]

Hi

During the upgrade I got the following warnings:

Setting up apt (0.9.7.9) ...
Installing new version of config file /etc/apt/apt.conf.d/01autoremove ...
Installing new version of config file /etc/cron.daily/apt ...
gpg: key B98321F9: "Squeeze Stable Release Key <debian-release@lists.debian.org>" not changed
gpg: key 473041FA: "Debian Archive Automatic Signing Key (6.0/squeeze) <ftpmaster@debian.org>" not changed
gpg: key 65FFB764: "Wheezy Stable Release Key <debian-release@lists.debian.org>" not changed
gpg: key 46925553: "Debian Archive Automatic Signing Key (7.0/wheezy) <ftpmaster@debian.org>" not changed
gpg: Total number processed: 4
gpg:              unchanged: 4
gpg: checking the trustdb
gpg: WARNING: digest algorithm MD5 is deprecated
gpg: please see http://www.gnupg.org/faq/weak-digest-algos.html for more information
gpg: no ultimately trusted keys found

These look like the report in bug #662948.
However, this bug was opened for version 0.8.15.10, and was closed 
with later versions of apt (my system has 0.9.7.9).

I really know nothing about gpg so I could not fully understand the 
report. But following-up on some remarks in the report I noted that

1. /usr/share/keyrings/debian-archive-removed-keys.gpg was changed.
2. Backup is in debian-archive-removed-keys.gpg~.
3. The permissions on all the files in /usr/share/keyrings/ are 644.

And that's it, I am at a dead-end.

Is this something to worry about?
Do you think bug #662948 has resrufaced?

Thanks in advance,
Itay