QuantifiedConstraints: Can't define class alias

{-# Language TypeInType, MultiParamTypeClasses, TypeFamilies, FlexibleContexts, FunctionalDependencies, AllowAmbiguousTypes, QuantifiedConstraints, GADTs, ConstraintKinds, KindSignatures, RankNTypes, FlexibleInstances, UndecidableInstances, TypeOperators #-}

import Data.Kind

class Reifies s a | s -> a where
  reflect :: proxy s -> a

newtype Lift :: forall k. (Type -> Constraint) -> Type -> k -> Type where
  Lift :: a -> Lift cls a s

data family Def :: (k -> Constraint) -> (k -> Type)

class    (forall s a. Reifies s (Def cls a) => cls (Lift cls a s)) => ReifiableConstraint cls
instance (forall s a. Reifies s (Def cls a) => cls (Lift cls a s)) => ReifiableConstraint cls

gives an error

$ ghci -ignore-dot-ghci Bug.hs
GHCi, version 8.5.20180128: http://www.haskell.org/ghc/  :? for help
[1 of 1] Compiling Main             ( /tmp/Bug.hs, interpreted )

/tmp/Bug.hs:14:10: error:
    • Could not deduce: cls (Lift cls a s)
        arising from the superclasses of an instance declaration
      from the context: forall (s :: k) a.
                        Reifies s (Def cls a) =>
                        cls (Lift cls a s)
        bound by the instance declaration at /tmp/Bug.hs:14:10-93
      or from: Reifies s (Def cls a)
        bound by a quantified context at /tmp/Bug.hs:1:1
    • In the instance declaration for ‘ReifiableConstraint cls’
   |
14 | instance (forall s a. Reifies s (Def cls a) => cls (Lift cls a s)) => ReifiableConstraint cls
   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Failed, no modules loaded.
Prelude> 

This is a rare occasion that the class alias trick fails for me so ~+~yay~+~. But is it intended?

Trac metadata

Trac field	Value
Version	8.5
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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