nasty things possible with generalized newtype deriving

Hello guys, are you following this Haskell Cafe thread: http://www.mail-archive.com/haskell-cafe@haskell.org/msg72300.html Seems that you can do ugly things with GHC’s current implementation of generalized newtype deriving. For example, you can easily construct sets with corrupted internal structure even if there are no bogus Ord instances. Best wishes, Wolfgang