Can't view package changelogs via update-manager

[Mark McCorkell <markmccorkell@tiscali.co.uk>]

Running unstable, recently update-manager (0.68.debian-7) is unable to
display changelogs for any available updates. Everything else (actualy
updating of package lists and downloading/installing packages) works
fine.

Error appears as:

srcpkg = pkg.sourcePackageName
Unhandled exception in thread started by <bound method
MyCache.get_changelog of <UpdateManager.UpdateManager.MyCache object at
0x1cec250>>
Traceback (most recent call last):
  File "/usr/lib/pymodules/python2.5/UpdateManager/UpdateManager.py",
line 162, in get_changelog
    section = pkg._depcache.GetCandidateVer(pkg._pkg).Section
AttributeError: 'Package' object has no attribute '_depcache'

preceded by several warnings about deprecated function calls.

Google gives only a couple of links to old bug reports on Ubuntu
launchpad, none of which seem to match what I'm getting. I don't know
much about apt beyond basic day-to-day usage, so anyone have any idea
whether this is a problem with my setup, and if so, where I might begin
looking for solutions?

TIA.

-- 
Mark McCorkell <markmccorkell@tiscali.co.uk>
"At least you can ignore my inanity, I'm stuck with it for life"