I exported the deck and did a sort -u on both import and export and deleted the unnecessary quote marks from the export.
sdiff on the sort results said that every line was different, but I could not see any difference. I piped sdiff into od -xc and could not find any differences.
So I tried head -2 /tmp/{IN,OUT} | od -xc and verified that the first lines are NOT different!
So, I imported the same (unsorted) unedited file again, and it again said “148 notes updated.” I did a check DB and imported again: same result.
If there is something in the import file that Anki doesn’t like and alters during import, I cannot find any evidence because either od -xc or diff/sdiff is giving false output!