$ cat z.go
package main

import "fmt"
import "reflect"

type I interface{ m() interface{ I } }

type J interface{ m() interface{ K } }
type K interface{ m() interface{ J } }

var i = reflect.TypeOf(new(interface{ I })).Elem()
var j = reflect.TypeOf(new(interface{ J })).Elem()
var k = reflect.TypeOf(new(interface{ K })).Elem()

func main() {
	if i != j || i != k || j != k {
		fmt.Println("FAIL")
		fmt.Println(i)
		fmt.Println(j)
		fmt.Println(k)
	}
}

$ go run z.go
FAIL
interface { main.m() interface { main.m@18 } }
interface { main.m() interface { main.m() interface { main.m@18 } } }
interface { main.m() interface { main.m() interface { main.m@18 } } }