"ghc-6.6: panic! (the 'impossible' happened) interactiveUI:flush" when hiding haskell98 and importing IO

I was trying to compile John Macheam's "GetOptions" with ghc-6.6. It failed saying

ben@sarun: .../repos/GetOptions > runhaskell Setup.hs build    
Preprocessing library GetOptions-1.0...
Building GetOptions-1.0...

GetOptions.hs:31:7:
    Could not find module `IO':
      it is a member of package haskell98, which is hidden

I exposed haskell98:

ben@sarun: .../repos/GetOptions > sudo ghc-pkg expose haskell98
Saving old package config file... done.
Writing new package config file... done.

But still no luck... Anyway then I said to myself "forget it, just use the hierarchical library stuff", hid haskell98 package again, and changed the import stuff a bit (see below). Result:

ben@sarun: .../repos/GetOptions > runhaskell Setup.hs build

<interactive>:1:84:
    Failed to load interface for `IO':
      it is a member of package haskell98, which is hidden
ghc-6.6: panic! (the 'impossible' happened)
  (GHC version 6.6 for x86_64-unknown-linux):
        interactiveUI:flush

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

This is the "fix" I applied:

ben@sarun: .../repos/GetOptions > darcs whatsnew
{
hunk ./GetOptions.hs 27
-import List
+import Data.List
hunk ./GetOptions.hs 30
-import System
-import IO
+import System.IO
+--import IO
}

Here is the repo I pulled from, so maybe you can reproduce the bug:

ben@sarun: .../repos/GetOptions > cat _darcs/prefs/defaultrepo 
http://repetae.net/john/repos/GetOptions

I could be that my ghc installation is completely screwed up but I wouldn't know how or why.

Ben

Trac metadata

Trac field	Value
Version	6.6
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Unknown
Architecture	Unknown