Problem with derived instances.

This code produces "True" with ghc-5.04.2 and ghc-5.02.3.   It works as I 
would expect it to with ghc-4.08.1.  Similarly, the derived instances of Ord 
also don't work.

The only time that I've found in my limited expermentation that equality 
returns false is:

Str "a" == Str "ab"

best,
leon

> infixr 3 :*
> infixr 2 :+
> 
> data RE a = RE a :+ RE a
>           | RE a :* RE a
>           | Cat  [RE a]
>           | Star (RE a)
>           | Plus (RE a)
>           | Opt  (RE a)
>           | Comp (RE a)
>           | Empty
>           | Str  [a]
>             deriving (Show, Eq, Ord)
> 
> main = print (Str "ab" == (Str "a" :+ Str "b"))