Try 'sort --debug -h -u' to see more.
I don't see a bug there, just an infelicity. -h means 'sort' should look
for a number, and your data lines don't start with numbers.
- bug#76290: "sort -u&qu... Rupert Gallagher via GNU coreutils Bug Reports
- bug#76290: "sort ... Paul Eggert
- bug#76290: "s... Rupert Gallagher via GNU coreutils Bug Reports
- bug#76290: &qu... Paul Eggert