[Haskell-beginners] Strange behavior

[Luca Ciciriello]

I found a strange behavior in my code 
 
Here a (very) simplified version of my code:

{-# LANGUAGE PArr #-}
{-# OPTIONS -fdph-seq #-}

module Main where

import Control.Parallel
import GHC.PArr

parArr :: [:String:]
parArr = [: "1", "2", "3", "4" :]

isElement :: String -> Bool
isElement x = x `elemP` parArr

main :: IO ()
main = do
          putStrLn $ (show . isElement) "5"

The aspected result is "False" ("5" isn't a member of parArr), but the result I get is "True".

I've compiled this code with the command:
ghc --make -Odph -threaded Test.hs -rtsopts -o test

and launched with:
test +RTS -N2

My system is MacOS X 10.7.1 with Xcode 4.1 and GHC 7.0.4 (I've found the same behavior on Windows).

Its obvious I'm missing something. Could someone help me?

Thanks.

Luca.