std/http/setCookie doesn't work?

import * as cookies from "https://deno.land/std@0.211.0/http/cookie.ts"
var h = new Headers()

cookies.setCookie(h, {name: 'foo', value: 'FOO'})
// Headers { "set-cookie": "foo=FOO" }
// OK (works as expected)

cookies.setCookie(h, {name: 'bar', value: 'BAR'})
// Headers { "set-cookie": "bar=BAR" }
// Not OK: Cookie `foo` was deleted for some reason!

cookies.setCookie(h, [{name: 'x', value: 'X'}, {name: 'y', value: 'Y'}])
// Headers { "set-cookie": "bar=BAR" }
// Not OK: None of the cookies were set