In reference to: http://groups.google.com/d/topic/golang-nuts/-vRM1B4z8bk/discussion

What steps will reproduce the problem?
Use utf8.DecodeRune or related functions to decode a 4-byte UTF-8 sequence, which
encodes a code point greater than utf8.MaxRune (U+10FFFF):

http://play.golang.org/p/Ii4RGZgkux

What is the expected output?
Each byte of the input should be treated as invalid, so utf8.DecodeRune(b[i:]) should
return (RuneError, 1) four times. This is what happens for a 5-byte input, such as
"\xFB\xBF\xBF\xBF\xBF" (U+3FFFFFF).

What do you see instead?
The input is decoded as U+1FFFFF, which is correct, but is not a valid code point.

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

Which operating system are you using?
Windows 7 64-bit

Which version are you using?  (run 'go version')
go version go1.0.2