Strange behavior of %A format with non-public discriminated unions

Question

The output of:

type Test =
  | First
  | Second
  | Third

let test = First

printf "test=%A" test

is

test=First

as expected, but if I declare the type internal:

type internal Test =
  | First
  | Second
  | Third

let internal test = First

printf "test=%A" test

the output becomes:

test=FSI_0019+Test

Is this by design? Why? Or a bug?

I am using Visual Studio 2010 with F# 2.0

Answer 1

To print non-public members use the '+' flag. The fact that it is missing in MSDN looks like doc issue:

printf "test=%+A" test