> What steps will reproduce the problem?
Given there are 2 go source files.

// source in ./foo/foo.go
package foo

type Elem struct {
    Name string
}

type Elems []Elem

// source in ./main.go
package main

import "./foo"
import "fmt"

func main() {
    fmt.Println(foo.Elems{
        foo.Elem{Name: "name"},
    })
}

# run go tool vet in command line
$ go tool vet main.go
main.go:7:17: ./foo.Elems struct literal uses untagged fields

> What is the expected output?
No vet error.

> What do you see instead?
Vet reports error as described above.

> Which compiler are you using (5g, 6g, 8g, gccgo)?
n/a

> Which operating system are you using?
$ uname -a
Darwin Huans-MacBook-Pro.local 12.2.0 Darwin Kernel Version 12.2.0: Sat Aug 25 00:48:52
PDT 2012; root:xnu-2050.18.24~1/RELEASE_X86_64 x86_64

> Which version are you using?  (run 'go version')
go 1.0.3

> Please provide any additional information below.
If I rewrite main.go as following, go tool vet will stop complaining.

func main() {
    fmt.Println(foo.Elems([]foo.Elem{  // explicitly write []foo.Elem here
        foo.Elem{Name: "name"},
    }))
}