Missing subst in instance declarations

This fails, but it looks right to me:
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE AllowAmbiguousTypes #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE ExistentialQuantification #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE FunctionalDependencies #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE MultiWayIf #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE RecordWildCards #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE StandaloneDeriving #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE TypeSynonymInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE UndecidableInstances #-}
{-# LANGUAGE UnicodeSyntax #-}
{-# LANGUAGE TemplateHaskell #-}

module Types (CatName(..), Category(..), ViewAPI(..), View(..), ViewPref(..), VPEntry(..)) where

import           Data.List (find)
import           GHC.Prim (Constraint)

type family   C a ∷ Constraint
type instance C a = (Eq a, Show a)

data CatName
   = Graph
   | Dag
   | Set
   deriving (Eq, Ord, Show, Read)

class C (ViewName cn) ⇒ Category (cn ∷ CatName) where
----- site of GHC 7.10.2 failure
   data ViewName cn ∷ *

instance Category 'Graph where
   data ViewName 'Graph = SideGraph | DownGraph deriving (Eq, Show)
instance Category 'Set where
   data ViewName 'Set   = Grid | List           deriving (Eq, Show)

class (Category cn) ⇒ ViewAPI (cn ∷ CatName) (vn ∷ ViewName cn) where

$(return [])

instance ViewAPI 'Set ('Grid ∷ ViewName cn) where
                      ----- site of the "nokinds" failure
goldfirere / ghc

Missing subst in instance declarations #44
