ghc5.04.1 deriving Read/Show broken

[George Russell]

With the attached file, on both Linux and Solaris, I get the following

----  Cut here -------
# ghci --interactive
   ___         ___ _
  / _ \ /\  /\/ __(_)
 / /_\// /_/ / /  | |      GHC Interactive, version 5.04.1, for Haskell 98.
/ /_\\/ __  / /___| |      http://www.haskell.org/ghc/
\____/\/ /_/\____/|_|      Type :? for help.

Loading package base ... linking ... done.
Loading package haskell98 ... linking ... done.
Prelude> :load GHCBug
Compiling GHCBug           ( GHCBug.hs, interpreted )
Ok, modules loaded: GHCBug.
*GHCBug> show (read (show (Commit 1 "1" Nothing)) :: Command)
"*** Exception: Prelude.read: no parse
----- Cut here ------------

NB (1) this seems to occur in ghc generally, not just in ghci.  (2) Read/Show being fairly
important to us, I'm afraid this means we will have to avoid using ghc5.04.1.  I hope 
ghc5.04.2 comes along soon.
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