"Install security updates without confirmation" does not make required configuration changes

[Oliver]

Ubuntu Release: 11.04
Package version: 0.80.9

If /etc/apt/apt.conf.d/50unattended-upgrades has been edited manually, e.g. the line:
"${distro_id} ${distro_codename}-security";
is commented out, then selecting "Install security updates without confirmation" will not re-enable this option as expected.