Getting stdout and stderr as a single handle from createProcess does not work on Windows

The following test case works on Linux (an as far as I know on Mac OS X too), but not on Windows.

{-# OPTIONS_GHC -fno-warn-missing-signatures #-}
module Spec (main) where
import           Test.HUnit
import           System.Process
import           System.IO

subprocess = concat $
  [ "module Main where\n"
  , "import System.IO\n"
  , "main = do\n"
  , "  hPutStr stderr \"foo\"\n"
  , "  hFlush stderr\n"
  , "  hPutStrLn stdout \"bar\"\n"
  , "  hFlush stdout\n"
  ]

main = runTestTT $ TestCase $ do
  (Just hin, Just hout, Nothing, _) <-
    createProcess $ (proc "runhaskell" []) {
        std_in = CreatePipe
      , std_out = CreatePipe
      , std_err = UseHandle stdout
    }
  hPutStrLn hin subprocess
  hClose hin
  line <- hGetLine hout
  line @?= "foobar"

Do we consider this a bug? If not, what would be the suggested way to do that?

Trac metadata

Trac field	Value
Version	7.2.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	libraries/process
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