N: Ignoring File *.save In Directory '/etc/apt/sources.list.d/' As It Has An Invalid Filename Extension

Just recently apt-get update started throwing errors which read:

N: Ignoring file 'google-chrome.list.save' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension
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N: Ignoring file 'google-musicmanager.list.save' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension

Looking inside directory  /etc/apt/sources.list.d/  I saw a number of files which ended with .save, which were not there before since my last apt-get update.
Apparently they are some sort of backup files, because the content of file foo.list.save is the same as file foo.list.

Following fix will work and next time you apt-get update these former notices won't be shown :

su -c "echo 'Dir::Ignore-Files-Silently:: \"(.save)$\";' > /etc/apt/apt.conf.d/99ignoresave" 

I recently installed software-properties-gtk and update-notifier, and I suspect one of these packages to generate these files with the .save extension.....