Wierd behavior of bytes.Join

Hi,

I have a test that I give as an input to my test program, I then use
readLine to read from the stdin with a buffer of 20 bytes. I have two
different versions of this, the first one [Version 1] uses a
two-dimensional slice which is appended and the joined via bytes.Join.
The second one [Version 2] uses a one-dimensional slice which is
appended to and then printed. The wierd thing is that they give
different output. See code below.

Is my code flawed or is this a bug?

Regards,
Josef

$ cat test
asdfghijklmnopqrstuvxyz

$ cat test | ./test-bug-readline
2012/05/23 10:58:23 asdfghijklmnopqrstuv
2012/05/23 10:58:23 xyz
2012/05/23 10:58:23 "xyz\nghijklmnopqrstuvxyz"
2012/05/23 10:58:23 Line was nil while reading from stdin

$ cat test | ./test-bug-readline
2012/05/23 11:00:39 asdfghijklmnopqrstuv
2012/05/23 11:00:39 xyz
2012/05/23 11:00:39 "asdfghijklmnopqrstuvxyz"
2012/05/23 11:00:39 Line was nil while reading from stdin

[version 1]
$ cat test-bug-readline.go
package main

import (
	"bufio"
        "bytes"
	"io"
	"log"
	"os"
)

func main() {
	r := bufio.NewReaderSize(os.Stdin, 20)
	alive := true
	lines := make([][]byte, 0)
	for alive {
		line, isPrefix, err := r.ReadLine()

		if line == nil {
			alive = false
			log.Fatalf("Line was nil while reading from stdin")
		}

		if err != nil {
			if err != io.EOF {
				log.Fatalf("Error was cought while reading from stdin, err: %s", err)
			}
			alive = false
		}

		if len(line) > 0 {
			log.Println(string(line))
			lines = append(lines, line)
		}

		if isPrefix {
			continue
		}
	
		if alive {
			log.Printf("%#v", string(bytes.Join(lines,nil)))
		}

		lines = make([][]byte, 0)
	}
}

[version 2]
$ cat test-bug-readline.go
package main

import (
	"bufio"
	"io"
	"log"
	"os"
)

func main() {
	r := bufio.NewReaderSize(os.Stdin, 20)
	alive := true
	lines := make([]byte, 0)
	for alive {
		line, isPrefix, err := r.ReadLine()

		if line == nil {
			alive = false
			log.Fatalf("Line was nil while reading from stdin")
		}

		if err != nil {
			if err != io.EOF {
				log.Fatalf("Error was cought while reading from stdin, err: %s", err)
			}
			alive = false
		}

		if len(line) > 0 {
			log.Println(string(line))
			lines = append(lines, line...)
		}

		if isPrefix {
			continue
		}
	
		if alive {
			log.Printf("%#v", string(lines))
		}

		lines = make([]byte, 0)
	}
}