Comment 9 for bug 515138

sudo rm /var/lib/update-notifier/user.d/ecryptfs-record-passphrase

... and the defunct processes are gone. At least on my laptop for a while now anyway.

It's a symlink to /usr/share/ecryptfs-utils/ecryptfs-record-passphrase which is an update-notifier "script" which seems to be a reminder for the user to make a note of the key used to encrypt the home directory. For some reason kubuntu-notifier-helper seems to choke on this file and cause defunct processes.

There is a catch though. Certain actions trigger the symlink to reappear. Ie. unplugging/replugging the AC power and the symlink is back.