Problem deriving instances

I have the following (reduced to the bare neccessities to produce the error) piece of code:

----
newtype A a = A a
    deriving (Eq,Show)

type B = A

type C = B D
--type C = A D
type D = Double

data E = E { a :: C }
    deriving (Eq,Show)
----

Compiling with ghc gives me the following error:
test.hs:13:
    No instance for `Eq C'
    When deriving classes for `E'

When I change the type of C to what I commented out (eg A D instead of B D) it works fine.

I don't think this is an error on my side, and besides hugs loads it without a complaint.

Trac metadata

Trac field	Value
Version	None
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	ResolvedFixed
Component	Compiler
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