This is unfortunate, but is a known bug that I don't think can be fixed
without either making `-l/--files-with-matches` much slower or changing
what "binary filtering" means by default.
In this PR, we document this inconsistency since users may find it quite
surprising. The actual work-around is to disable binary filtering with
the `--binary` flag.
We add a test confirming this behavior.
Closes#3131