Synaptic presents an ugly error regarding .save files

When updating the repositories on Maverick, I often get an error messages like:

N: Ignoring file 'google-chrome.list.distUpgrade' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension
N: Ignoring file 'canonical-dx-team-une-lucid.list.distUpgrade' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension
N: Ignoring file 'ubuntu-wine-ppa-lucid.list.save' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension
N: Ignoring file 'medibuntu.list.distUpgrade' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension
N: Ignoring file 'canonical-dx-team-une-lucid.list.save' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension
N: Ignoring file 'ricotz-testing-maverick.list.save' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension
N: Ignoring file 'ubuntu-mozilla-daily-ppa-lucid.list.save' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension
N: Ignoring file 'ubuntu-wine-ppa-lucid.list.distUpgrade' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension

The problem can temporarily be solved by running these commands:

cp /etc/apt/sources.list.d/
sudo rm *.save
sudo rm *.distUpgrade

... but something (Synaptic) creates these files again and then complains about them next time you update ;)