Comment 19 for bug 1173209

Yeah, looking at /usr/lib/ubuntu-release-upgrader/release-upgrade-motd, it never expires the cache if it's non-zero-length, which could also pose a problem if we want to allow people to skip releases in the future, as it would never update from, say, 12.10 to 13.04 or whatever.

Definitely an issue in this case, though, as it will never go back to zero-length after an upgrade, so it should definitely be either deleted or emptied on upgrade.