Why don't Software and Updates & add-apt-repository --remove delete PPA files?

I observe that removing a ppa with Software & Updates or with :

sudo add-apt-repository --remove ppa:xxx/yyy

merely empties the file one wants to remove and leaves an empty theuglyppa.list file in /etc/apt/sources.list.d/ (same with ppa-purge) Why is this ? This seem quite illogical to keep such residue especially for newbies who won't know that they should add :

sudo rm /etc/apt/sources.list.d/theuglyppa.list*

to their cleaning procedure. Where should this odd behaviour be reported as a bug ? As I consider this as a bug, unless somebody tells me what brilliant logic justifies such leftovers.