Comment 28 for bug 756317

With the current situation, you do not even have to actively use APT behind such a portal for the bug to be triggered.
When my main internet connection was working with such a portal, APT just stopped working seemingly randomly because there apparently is some kind of auto fetch daemon running by default on Ubuntu. I had to delete the contents of that directory very regularly, because APT often wasn't working when I needed it. Of course I would only use APT myself once I verified that my connection was working properly.

And I'm sad to say it, but it seems such portals are very popular in this part of the world :(

If this is not going to be fixed for Trusty, at least add a note to the release notes which explains how to disable this automatic fetching of package lists. That would significantly reduce the problem for many people.