worker-wrapper/iface trouble

[Sven Panne]

HOpenGL's saga through GHC bugs still continues! :-)
Something strange (worker-wrapper related?) is going on in
before-ghci-branch with a ghc-4.09 built a week ago:

--------------------------------------------------
module Foo where

import Foreign

inParam :: Storable a => (Ptr a -> IO b) -> a -> IO b
inParam act x = do
   buf <- malloc
   poke buf x
   val <- act buf
   free buf
   return val
--------------------------------------------------
module Bar where

import Foreign
import Foo

marshallBool :: Bool -> Int
marshallBool False = 1234
marshallBool True  = 5678

lightModel :: Either Int Bool -> IO ()
lightModel (Left  i) = inParam (glLightModelfv 1111) i
lightModel (Right b) = glLightModeli 3333 (marshallBool b)

foreign import glLightModeli  :: Int -> Int     -> IO ()
foreign import glLightModelfv :: Int -> Ptr Int -> IO ()
--------------------------------------------------
module Baz(module Bar) where
import Bar
--------------------------------------------------

(ignore the "implicit declaration" warnings, could be fixed by -#include <GL/gl.h>)

--------------------------------------------------
jeanluc:/usr/src/packages/BUILD/fptools/hslibs/OpenGL/GL # ghc -O -fglasgow-exts -c Foo.hs
jeanluc:/usr/src/packages/BUILD/fptools/hslibs/OpenGL/GL # ghc -O -fglasgow-exts -c Bar.hs
ifaceBinds: free vars: zdwzdj_s3lZ
In file included from /tmp/ghc5262.c:4:
/tmp/ghc5262.hc: In function `Bar_zdwlvl_fast2':
/tmp/ghc5262.hc:50: warning: implicit declaration of function `glLightModelfv'
/tmp/ghc5262.hc: In function `Bar_zdwccall1_fast3':
/tmp/ghc5262.hc:287: warning: implicit declaration of function `glLightModeli'
jeanluc:/usr/src/packages/BUILD/fptools/hslibs/OpenGL/GL # ghc -O -fglasgow-exts -c Baz.hs

Baz.hs:1:
    Failed to find interface decl for `Bar.$w$j'
    from module `Bar'

Compilation had errors
--------------------------------------------------

Apart from a fix for this, I'd appreciate a few lines explaining the
worker-wrapper stuff in GHC or a pointer to a paper etc. I'd like to
fix bugs like that myself, if I only knew how...  :-}

Cheers,
   Sven