Comment 148 for bug 659438

In Precise the issue doesn't appear since there is a race between the
simulate() and the run() method which eats the exception. This race
situation has been fixed in trunk recently that hasn't been uploaded
yet.

Furthermore aptdaemon trunk now catches the exception in the
apt.cache.Cache.required_download call and lets the transaction fail
with an ERROR_INCOMPLETE_INSTALL. So we won't get any bug reports of
this anymore - although the issue isn't fixed on the lower level
(debconf/apt).

Unfortunately software-center doesn't handle the
ERROR_INCOMPLETE_INSTALL correctly yet. It just displays the error
message but doesn't offer to run the FixIncompleteInstall() method of
aptdaemon which would basically run "dpkg --configure -a" and fix the
system.

Additionally the current error message doesn't contain any hind to run
sudo dpkg --configure -a manually.

But it seems to be a first step to resolve the issue. I will try to
create a working patch for s-c in the next days.