Mismatched contexts

Hello,

I observed the following behavior on GHC-6.0.1 and CVS HEAD.
With -fglasgow-exts the following program


data Functions =
    Functions { f1, f2 :: Integral a => a -> a }

functions :: Functions
functions =
    Functions { f1 = (\x -> x),
                f2 = f2b
              }

f2a, f2b :: Integral a => a -> a

f2a = f1 functions
f2b x = x


is accepted by GHC, but if I change
  f2 = f2b
to
  f2 = f2a
in the definition of `functions', GHC says

    Mismatched contexts
    When matching the contexts of the signatures for
      functions :: Functions
      f2a :: forall a. (Integral a) => a -> a
    The signature contexts in a mutually recursive group
      should all be identical
    When generalising the type(s) for functions, f2a

(This can be "fixed", as I found out, by adding a dummy type
variable to the Functions data type:

  data Functions dummy = ...
  functions :: Integral dummy => Functions dummy
)

I don't understand why the contexts must be identical in mutually recursive 
definitions. `f2a' should have the right type, since it is explicitly 
declared to have the same type as `f2b'. Is GHC wrong here, or am I 
misunderstanding something?

Regards,
Armin