Allow me to disagree.

I mean, obviously, it's not "breaking specifications", as there does NOT seem to be available specifications (because the documentation does NOT seem to mention how "sort" orders elements), but still, it furiously looks like an unwanted behaviour, or, at the very least, a caveat worth mentioning.

I'm guessing that adding a single paragraph to the documentation, telling that a positive result orders in the following way, a negative result orders in the other way, and a null result keeps the same order, and that it is STRONGLY RECOMMENDED to use the binary comparison operator for this, to avoid potential problems, would do the trick.

Because, I'll be blunt, but I had no recollection whatsoever of having previously worked with the "comparison" operator. And if it's not explained why one should use it, then... why not use something more familiar, and doing the same thing ? I mean, this is Perl, and "There is more than one way to do it", right ?