multios doesn't work with 2>&1

[Han Pingtian <hanpt@xxxxxxxxxxxxxxxxxx>]

Hello,

According to the zsh guide's "2.5.8 ‘Go faster’ options for power
users", page 44:

    % echo foo 2>&1 >/dev/null | sed 's/foo/bar/'

should output "bar" if multios has been set. But it outputs nothing
here. But if I removed the "2>&1", then it works just fine:

    % echo foo >/dev/null | sed 's/foo/bar/'
    bar

Please have a look. Thanks.