Comment 4 for bug 91368

[UPD] I downloaded the problematic packages list file, gunzip, rename and move it into '/var/lib/apt/lists' manually, and it works fine. But it is not a way I liked.

Finally, this solution: http://ubuntuforums.org/archive/index.php/t-9944.html (replace 'http://' protocol in the 'sources.list' to 'ftp://') fixed the problem. It seems it's a apt+proxy issue (though I have no idea why the same file is downloaded by wget just fine but corrupted when downloaded by apt)