Modernized sources not handled for official package repositories

mintsources won't recognize that the official package repositories .list has been converted to .sources format using apt modernize-sources and will just create a default .list file again, which will not only dismiss previous settings and mirrors, but also causes a heap of apt warnings because of duplicate entries:

Warning: Target Packages (main/binary-amd64/Packages) is configured multiple times in /etc/apt/sources.list.d/official-package-repositories.list:5 and /etc/apt/sources.list.d/official-package-repositories.sources:4
Warning: Target Packages (main/binary-i386/Packages) is configured multiple times in /etc/apt/sources.list.d/official-package-repositories.list:5 and /etc/apt/sources.list.d/official-package-repositories.sources:4
Warning: Target Packages (main/binary-all/Packages) is configured multiple times in /etc/apt/sources.list.d/official-package-repositories.list:5 and /etc/apt/sources.list.d/official-package-repositories.sources:4
Warning: Target Translations (main/i18n/Translation-en_US) is configured multiple times in /etc/apt/sources.list.d/official-package-repositories.list:5 and /etc/apt/sources.list.d/official-package-repositories.sources:4
Warning: Target Translations (main/i18n/Translation-en) is configured multiple times in /etc/apt/sources.list.d/official-package-repositories.list:5 and /etc/apt/sources.list.d/official-package-repositories.sources:4
Warning: Target DEP-11 (main/dep11/Components-amd64.yml) is configured multiple times in /etc/apt/sources.list.d/official-package-repositories.list:5 and /etc/apt/sources.list.d/official-package-repositories.sources:4
Warning: Target DEP-11 (main/dep11/Components-all.yml) is configured multiple times in /etc/apt/sources.list.d/official-package-repositories.list:5 and /etc/apt/sources.list.d/official-package-repositories.sources:4
Warning: Target Contents-deb (main/Contents-amd64) is configured multiple times in /etc/apt/sources.list.d/official-package-repositories.list:5 and /etc/apt/sources.list.d/official-package-repositories.sources:4
Warning: Target Contents-deb (main/Contents-i386) is configured multiple times in /etc/apt/sources.list.d/official-package-repositories.list:5 and /etc/apt/sources.list.d/official-package-repositories.sources:4
Warning: Target Contents-deb (main/Contents-all) is configured multiple times in /etc/apt/sources.list.d/official-package-repositories.list:5 and /etc/apt/sources.list.d/official-package-repositories.sources:4
Warning: Target Packages (contrib/binary-amd64/Packages) is configured multiple times in /etc/apt/sources.list.d/official-package-repositories.list:5 and /etc/apt/sources.list.d/official-package-repositories.sources:4
Warning: Target Packages (contrib/binary-i386/Packages) is configured multiple times in /etc/apt/sources.list.d/official-package-repositories.list:5 and /etc/apt/sources.list.d/official-package-repositories.sources:4
Warning: Target Packages (contrib/binary-all/Packages) is configured multiple times in /etc/apt/sources.list.d/official-package-repositories.list:5 and /etc/apt/sources.list.d/official-package-repositories.sources:4
[...]

mintsources 2.3.6, LMDE7

Start by locating the mintsources code that handles official-package-repositories.list and repository files under /etc/apt/sources.list.d. Reproduce the LMDE7 case with an official-package-repositories.sources file created by apt modernize-sources. Done means existing .sources settings and mirrors are preserved, no duplicate .list is created, and the apt warnings no longer occur.