by AwakenRz:

Before filing a bug, please check whether it has been fixed since the
I think it should already been fixed long ago. But I cannot find the issue tracking
status.

Run "go version" and compare against
go version go1

Thanks.

What steps will reproduce the problem?
If possible, include a link to a program on play.golang.org.
1 Run the following program:
package main

import (
    "bytes"
    "encoding/gob"
    "fmt"
)

type P interface {
    Q()
}

type A struct {
    J P
}

type B struct {
    P int
}

func (b *B) Q() {
}

func main() {
    b := B{2}
    c := A{&b}
    gob.Register(A{})
    gob.Register(B{})
    var buffer bytes.Buffer
    en := gob.NewEncoder(&buffer)
    if err := en.Encode(&c); err != nil {
        panic(err.Error())
    }
    buff := bytes.NewBuffer(buffer.Bytes())
    de := gob.NewDecoder(buff)
    if err := de.Decode(&c); err != nil {
        fmt.Println(err.Error())
    } else {
        fmt.Println(c)
    }
}

What is the expected output?
Should throw no errors

What do you see instead?
A runtime error saying gob: cannot assign value of type main.B to main.P

Which compiler are you using (5g, 6g, 8g, gccgo)?
6g

Which operating system are you using?
Mac OSX 10.7.4

Which version are you using?  (run 'go version')
go version go1

Please provide any additional information below.
Related discussion can be found 
https://groups.google.com/d/topic/golang-nuts/nl3GMEoT1KU/discussion
https://groups.google.com/d/topic/golang-nuts/2EFErFqpNwI/discussion