Comment 8 for bug 438279

From my unlearned investigation this seems to be related to this change in apt 0.7.22:
"...
  * apt-pkg/deb/dpkgpm.cc:
...
    - send "dpkg-exec" message on the status fd when dpkg is run
..."
I think that method "/usr/lib/python2.6/dist-packages/apt/progress/__init__.py, line 277, in updateInterface" wrongly parses this message as a regular package installation status. The message causing this error is:
"pmstatus:dpkg-exec:0:Running dpkg"
HTH