Comment 1:

you can't actually return a untyped constant "type" from a function,
so 0 here must be treated as some type, as the context doesn't specify
which integer type to use, it defaults to int.

Status changed to WorkingAsIntended.

Comment 2:

I agree one cannot return an untyped constant from a function, but one can "use" the
untyped constant 0 in many ways. For example, the following code is correct
func Foo() float64 {
    return 0
}
Here, 0 is used as a float64, not as an int. Thus, it seems like the error message
should be 
"cannot use 0 (untyped constant literal) as type []float64 in return argument"
One may never use an int as a float64, but one may use an untyped constant literal as a
float64

Comment 3:

Labels changed: added repo-main, release-none.

Status changed to Accepted.

Comment 4:

Here is another example of the same problem but in a different context
http://play.golang.org/p/2YtAt2ZXvX