[xinn]

This behavior is explicitly defined in the godoc for io. I don’t see why the author should be "stunned" by a function doing exactly what it says it does.

[nwp90]

That'll be because it's only been in the docs since they reported their issue.

[thirsteh]

You're both correct. It's been in the docs for io.Copy for a long time, and was only recently added to the http docs.