go tip (just after the 1.2 RC):

What steps will reproduce the problem?
Code (not in play because uses tip/1.2RC feature):

    package main
    import "fmt"
    func main() { fmt.Printf("%[3]s %[1]s %s\n", "woo", "world!") }

What is the expected output?

    %!s(BADINDEX) woo world!

What do you see instead?

    %!s(BADINDEX) %!s(BADINDEX) %!s(BADINDEX)

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

6g

Which operating system are you using?

Darwin/amd64 (MacOS 10.8.5)

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

go version devel +ebd02fba267b Fri Sep 20 09:40:56 2013 -0700 darwin/amd64

Please provide any additional information below.

The badindex means that this might be deemed as "buggy code", but I think it
*should* have handled the subsequent _good_ index and only shown the BADINDEX for the
first %[indexed]s parameter.