Because I [remove](https://github.com/bar/cakephp/commit/aa1aac9682d6e5543f8775c431fd2f23a95cac28#diff-b8a4043bec5d20830b77d240ae8fdef5L2442) it from ```fields()``` to make it easier to avoid duplicating virtual fields when trying to remove them from the fields array.

That was the only meaning of the ```array_unique()``` [here](https://github.com/bar/cakephp/commit/aa1aac9682d6e5543f8775c431fd2f23a95cac28#diff-b8a4043bec5d20830b77d240ae8fdef5L2514)