What steps will reproduce the problem?
http://play.golang.org/p/u5jfNgQH4Z

What is the expected output?
error parsing "=?iso-8859-2?Q?Bogl=E1rka_Tak=E1cs?=
<unknown@gmail.com>": mail: missing word in phrase (mail: charset not
supported: "iso-8859-2")

What do you see instead?
error parsing "=?iso-8859-2?Q?Bogl=E1rka_Tak=E1cs?=
<unknown@gmail.com>": mail: missing word in phrase

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

Which operating system are you using?
linux

Which version are you using?  (run 'go version')
1.1.2 linux/amd64

Please provide any additional information below.

http://tip.golang.org/src/pkg/net/mail/message.go?s=3592:3643#L361

   361      // Ignore any error if we got at least one word.
   362      if err != nil && len(words) == 0 {
   363          debug.Printf("consumePhrase: hit err: %v", err)
   364          return "", errors.New("mail: missing word in phrase")
   365      }
   366      phrase = strings.Join(words, " ")
   367      return phrase, nil

That seems wrong, the comment disagrees with the code.
The result being that if you got an error that prevented you from reading at least one
word it gets swallowed up.

Something like (line 364):
   364          return "", fmt.Errorf("mail: missing word in phrase (%s)", err)

would be much more informative.