Non-sensical error message when compiling with PolyKinds and a type family

When I compile the following code:

{-# LANGUAGE TypeFamilies,
             PolyKinds,
             ScopedTypeVariables
 #-}

convert :: a -> b
convert = undefined

type family Foo a 
type instance Foo Int = Bool

bar :: forall a b c dummya. (b -> c) -> ((Foo a) -> c)
bar f = (convert f :: (Foo a) -> c)

I get the following error message:

Sandbox.hs:13:34:
    Kind mis-match
    Expected kind `OpenKind', but `c' has kind `b'
    In an expression type signature: (Foo a) -> c
    In the expression: (convert f :: (Foo a) -> c)
    In an equation for `bar': bar f = (convert f :: (Foo a) -> c)

This error message does not make sense, for 'b' isn't a kind. It is interesting to note that removing dummya from the list of declared type variables changes the error to a GHC panic.

Trac metadata

Trac field	Value
Version	7.4.1-rc1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
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