Decode json to byte field (base64 encoded string) and re-encode gives a result different from the start json

weird_encode_decode.go

package main

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


type Obj struct {
    Value []byte `json:"value"`
}

func main() {

	data_arr := [][]byte {
		[]byte("{\"value\":\"ose=\"}"),
		[]byte("{\"value\":\"osa=\"}"),
		[]byte("{\"value\":\"osc=\"}"),
		[]byte("{\"value\":\"osY=\"}"),
	}
	
	for _, data := range data_arr {
		runTests(data)
	}
}

func runTests(data []byte) {
	fmt.Println("Original: ", string(data))
	fmt.Printf("After Decode and Encode: ")
	tryDecode(data)
	fmt.Println()
}

func tryDecode(data []byte) {
	obj := Obj{}

	r := bytes.NewReader(data)
	err := json.NewDecoder(r).Decode(&obj)

	if err != nil {
		fmt.Printf("err1: ")
		fmt.Println(err)
	} else {
		buf := new(bytes.Buffer)
		err := json.NewEncoder(buf).Encode(obj)

		if err != nil {
			fmt.Printf("err2: ")
			fmt.Println(err)
		} else {
			fmt.Printf(buf.String())
		}
	}
}