GHC Panic compiling type family with -XPolyKinds

I received the following error message:

ghc: panic! (the 'impossible' happened)
  (GHC version 7.4.0.20111219 for x86_64-unknown-linux):
        tyConKind ghc-prim:GHC.Prim.BOX{(w) tc 347}

I was compiling the following code:

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

convert :: a -> b
convert = undefined

type family Foo a

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

Interestingly, the output is different when changing the order in the forall (forall b a produces a different error). The same result happened on Linux/x86_64 and MacOS 10.7.2/x86_64-apple-darwin,

Trac metadata

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