runtime error with newtype declarations

[epsilonhalbe]

Here is a minimal showcase of the error I am facing:

If I declare a newtype datatype - then flags produce runtime errors. For data-declarations everything seems to work just fine.

{-# LANGUAGE DeriveDataTypeable #-}
module Main where

import System.Console.CmdArgs
---------------------------------------------------------------------------------
--                 Newtypes seem to make problems with CMDARGS                 --
---------------------------------------------------------------------------------

newtype NewtypeSample = NewtypeSample {helloNT :: FilePath } deriving (Show, Data, Typeable)

worksNT = NewtypeSample{helloNT = def &= help "World argument" }
         &= summary "NewtypeSample v1"

doesn'tWorkNT1 = NewtypeSample{helloNT = def &= help "World argument" &= opt "world" &= typFile}
         &= summary "NewtypeSample v1"

doesn'tWorkNT2 = NewtypeSample{helloNT = def &= help "World argument" &= opt "world"}
         &= summary "NewtypeSample v1"

---------------------------------------------------------------------------------
--                  Data declarations seem to work just fine                   --
---------------------------------------------------------------------------------

data DataSample = DataSample {helloD :: FilePath } deriving (Show, Data, Typeable)

worksD1 = DataSample{helloD = def &= help "World argument" &= opt "world"}
         &= summary "DataSample v1"

worksD2= DataSample{helloD = def &= help "World argument" &= opt "world" &= typFile}
         &= summary "DataSample v1"

main :: IO ()
main = do 
  print =<< cmdArgs doesn'tWorkNT1
  print =<< cmdArgs doesn'tWorkNT2
  print =<< cmdArgs worksNT
  print =<< cmdArgs worksD1
  print =<< cmdArgs worksD2
  return ()

Here are the errors I get:

• doesn'tWorkNT1

stack build && stack exec -- cmdargsbug
cmdargsbug-0.1.0.0: build (exe)
Preprocessing executable 'cmdargsbug' for cmdargsbug-0.1.0.0...
[1 of 1] Compiling Main             ( src/Main.hs, .stack-work/dist/x86_64-linux/Cabal-1.24.2.0/build/cmdargsbug/cmdargsbug-tmp/Main.o )
Linking .stack-work/dist/x86_64-linux/Cabal-1.24.2.0/build/cmdargsbug/cmdargsbug ...
cmdargsbug-0.1.0.0: copy/register
Installing executable(s) in
..../cmdargsbug/.stack-work/install/x86_64-linux/lts-8.17/8.0.2/bin
cmdargsbug: System.Console.CmdArgs.Implicit, unexpected mode: FlagType "FILE"
CallStack (from HasCallStack):
  error, called at ./System/Console/CmdArgs/Implicit/Local.hs:106:11 in cmdargs-0.10.17-IWa8ygdJhnJBShkQXN8V9I:System.Console.CmdArgs.Implicit.Local

commenting out the doesn'tWorkNT1 line produces

• doesn'tWorkNT2

stack build && stack exec -- cmdargsbug
cmdargsbug-0.1.0.0: build (exe)
Preprocessing executable 'cmdargsbug' for cmdargsbug-0.1.0.0...
[1 of 1] Compiling Main             ( src/Main.hs, .stack-work/dist/x86_64-linux/Cabal-1.24.2.0/build/cmdargsbug/cmdargsbug-tmp/Main.o )
Linking .stack-work/dist/x86_64-linux/Cabal-1.24.2.0/build/cmdargsbug/cmdargsbug ...
cmdargsbug-0.1.0.0: copy/register
Installing executable(s) in
..../cmdargsbug/.stack-work/install/x86_64-linux/lts-8.17/8.0.2/bin
cmdargsbug: System.Console.CmdArgs.Implicit, unexpected mode: FlagOptional "world"
CallStack (from HasCallStack):
  error, called at ./System/Console/CmdArgs/Implicit/Local.hs:106:11 in cmdargs-0.10.17-IWa8ygdJhnJBShkQXN8V9I:System.Console.CmdArgs.Implicit.Local