1. What version of Go are you using (go version)?
   master
2. What operating system and processor architecture are you using (go env)?
   tried on plan9_arm, linux_amd64, and darwin_amd64
3. What did you do?

package main

import (
    "os"
)

func main() {
    attr := &os.ProcAttr{Files: []*os.File{os.Stdin, os.Stdout, os.Stderr}}
    _, e := os.StartProcess("/no/such/command", nil, attr)
    if e != nil {
        println("1 FAIL: " + e.Error())
    } else {
        println("1 OK")
    }
    attr = &os.ProcAttr{Files: []*os.File{os.Stdin, os.Stderr, os.Stdout}}
    _, e = os.StartProcess("/no/such/command", nil, attr)
    if e != nil {
        println("2 FAIL: " + e.Error())
    } else {
        println("2 OK")
    }
}

1. What did you expect to see?

1 FAIL: fork/exec /no/such/command: ...
2 FAIL: fork/exec /no/such/command: ...

1. What did you see instead?

1 FAIL: fork/exec /no/such/command: ...
2 OK

In syscall.forkAndExecInChild, a comment don't stomp on pipe refers to avoiding a collision between nextfd (a temporary file descriptor used for permuting the order of fds for the child) and pipe (the file descriptor of the pipe used to report exec status back to the parent). Unfortunately the code doesn't quite live up to the promise of the comment.

Moving the referenced code to a more strategic place in the loop body is probably the tidiest correction. A suggested CL will follow shortly.