Comment 4 for bug 963533

Yes, we know for sure that purge & reinstall fixes the problem...that's our advice to affected users.

But the packaging system is supposed to work automatically, and we rely on that to maintain tens of thousands of machines. (Though obviously not that much is running precise right now.) This issue will automatically become irrelevant in a short amount of time; my real question is that I'd like to understand how it could happen.

A lucid=>precise upgrade shouldn't produce this problem; I think it's specific to the 2.3.1+dfsg-3ubuntu1 package which was momentarily available on precise.