I had such a similar issue when upgrading from Edgy to Feisty.  After the upgrade, a "sudo apt-get dist-upgrade" would look like this:
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chris@easyweaze:~$ sudo apt-get dist-upgrade
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Calculating upgrade... Done
The following packages will be upgraded:
  python-clearsilver
1 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 0B/169kB of archives.
After unpacking 397kB of additional disk space will be used.
Do you want to continue [Y/n]? y
(Reading database ... 31042 files and directories currently installed.)
Preparing to replace python-clearsilver 0.9.13-3.2ubuntu1 (using .../python-clearsilver_0.10.3-4.1_i386.deb) ...
Unpacking replacement python-clearsilver ...
dpkg: error processing /var/cache/apt/archives/python-clearsilver_0.10.3-4.1_i386.deb (--unpack):
 trying to overwrite `/usr/lib/python2.4/site-packages/neo_cgi.so', which is also in package python2.4-clearsilver
dpkg-deb: subprocess paste killed by signal (Broken pipe)
Errors were encountered while processing:
 /var/cache/apt/archives/python-clearsilver_0.10.3-4.1_i386.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)
-------------------------------------------------------------------------

A simple "sudo apt-get remove python2.4-clearsilver" didn't fix the problem, as I'd expect.  I had to remove both python2.4-clearsilver and python-clearsilver, which in turn removed trac, as well.  So, I fixed the problem like this:
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chris@easyweaze:~$ sudo apt-get remove python2.4-clearsilver python-clearsilver 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages will be REMOVED:
  python-clearsilver python2.4-clearsilver trac
0 upgraded, 0 newly installed, 3 to remove and 0 not upgraded.
Need to get 0B of archives.
After unpacking 2367kB disk space will be freed.
Do you want to continue [Y/n]? y
(Reading database ... 31041 files and directories currently installed.)
Removing trac ...
dpkg - warning: while removing trac, directory `/usr/share/trac/wiki-macros' not empty so not removed.
dpkg - warning: while removing trac, directory `/usr/share/trac' not empty so not removed.
Removing python-clearsilver ...
Removing python2.4-clearsilver ...
chris@easyweaze:~$ sudo apt-get install 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
chris@easyweaze:~$ sudo apt-get install trac
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following extra packages will be installed:
  python-clearsilver
Suggested packages:
  python-docutils
Recommended packages:
  python-setuptools
The following NEW packages will be installed:
  python-clearsilver trac
0 upgraded, 2 newly installed, 0 to remove and 0 not upgraded.
Need to get 0B/554kB of archives.
After unpacking 2544kB of additional disk space will be used.
Do you want to continue [Y/n]? y
Selecting previously deselected package python-clearsilver.
(Reading database ... 30759 files and directories currently installed.)
Unpacking python-clearsilver (from .../python-clearsilver_0.10.3-4.1_i386.deb) ...
Selecting previously deselected package trac.
Unpacking trac (from .../archives/trac_0.10.3-1_all.deb) ...
Setting up python-clearsilver (0.10.3-4.1) ...
Setting up trac (0.10.3-1) ...

chris@easyweaze:~$ 
-------------------------------------------------------------------------

Is it possible that python2.4-clearsilver is not a package that was ever in the Ubuntu repositories (and perhaps the same for python2.4-pythoncard)?  I don't remember, myself, whether I may have picked up that package from some third party, such as the Trac homepage (?).  There seems to be no "bugs page" for either of those packages; both of these links give you an "OOPS":
https://bugs.launchpad.net/ubuntu/+source/python2.4-pythoncard
https://bugs.launchpad.net/ubuntu/+source/python2.4-clearsilver
Wouldn't those bug pages exist even if those packages do not exist in Feisty, but existed in previous releases?