Re: "From which it follows that the docs were unclear. "
is this simply a case where Fred was the first to read the manuals, he wrote about it and didn't get it quite right then others have simply thought, "Sod reading the manuals, this looks OK.", tested it and it works.
Hang on, I'm not involved :)
(a) The number of years since I was that close to a CPU in programming is measured in decades and (b) it then involved a mere 8 bit chip.
I plead the Shaggy defense :)