nala fetch on Linux Mint: nala-sources.list keeps conflicting with official-package-repositories.list

Description of the issue and how to replicate it

When I set up the base mirror in Linux Mint's "Software Sources" app, I obviously choose the fastest one available, and it gets added into official-package-repositories.list. However, when I then fetch sources for nala, the resulting list, too, contains the same mirror. And if include it into the nala-sources.list and then try to e.g. nala update, I get a bunch of copies of the following warning:

Warning: Target [CNF/Packages/DEP-11/Translations etc.] is configured multiple times in /etc/apt/sources.list.d/nala-sources.list:[line number] and /etc/apt/sources.list.d/official-package-repositories.list:[line number]

Expected behavior

nala fetch would ignore the mirrors listed in official-package-repositories.list or maybe suppress these warnings instead

Current workaround

Manually deselect the conflicting mirror from the list returned by nala fetch