method definitions fail to refer to method-context classes

Sorry in advance if this is my lack of understanding...[[BR]] The following code fails:[[BR]]

class Cfoo a where
    f :: Int -> a -> Int

data Foo = F Int

instance Cfoo Foo where
    f m (F n) = m + n

data Bar = B Int

class Cbar a where
    g :: (Cfoo b) => a -> b

instance Cbar Bar where
    g (B m) = F m

with error:[[BR]]

Couldn't match expected type `b' against inferred type `Foo'
      `b' is a rigid type variable bound by
          the type signature for `g' at [...]
    In the expression: F m
    In the definition of `g': g (B m) = F m
    In the instance declaration for `Cbar Bar'

It's as if the "instance Cfoo Foo" statement is ignored when processing "instance CBar Bar"

Trac metadata

Trac field	Value
Version	6.12.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
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