ghc-pkg: can't unregister - not found - describe works?

[Marc Weber]

marc at localhost /pr/source/wxh/wxhaskell-0.9.4 $  ghc-pkg-wrapper-6.6.1 unregister wx
ghc-pkg: cannot find package wx
marc at localhost /pr/source/wxh/wxhaskell-0.9.4 $  ghc-pkg-wrapper-6.6.1 describe wx
name: wx
version: 0.10.1
license: AllRightsReserved
[...]

What does happen here?
ghc-pkg-wrapper is just a simple script defining GHC_PACKAGE_PATH

marc at localhost /pr/source/wxh/wxhaskell-0.9.4 $  ghc-pkg-wrapper-6.6.1 list
/nix/store/q74q9piy9fsk4k7w1p3r3xc8wsm1z87m-ghc-6.6.1/lib/ghc-6.6.1/package.conf:
    Cabal-1.1.6.2, HUnit-1.1.1, QuickCheck-1.0.1, base-2.1.1,
    [...]
/nix/store/fbj85ijnbc69bh19zi1a14p9idknb5g9-wxHaskell-0.10.1-pre20070124/nix-support/package.conf:
    wx-0.10.1, wxcore-0.10.1

Marc