Lazy application gives "No instance" error while strict application works

This might make sense if there were any IO. Here's the code:

{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE FunctionalDependencies #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE OverlappingInstances #-}
{-# LANGUAGE UndecidableInstances #-}

import Data.Maybe (isJust)

data Wrapper a = Wrapper a deriving (Show)

class Resolution a
instance Resolution (Wrapper a)

class (Resolution b, Resolution d) => C a b c d | a -> b, c -> d, a d -> c, b c -> a where
  cfun :: (b -> d) -> a -> c

instance (Resolution b, Resolution d, a ~ b, c ~ d) => C a b c d where
  cfun = ($)

instance (Eq a, C b c d e) => C (Maybe a -> b) c (Maybe a -> d) e where
  cfun f b = \x -> cfun f (b x)

foo :: Maybe a -> Wrapper Bool
foo = Wrapper . isJust

Applying Nothing strictly or in a let clause gives the expected answer (I expect that cfun id foo would be equivalent to foo):

*Main> cfun id foo $! Nothing
Wrapper False

*Main> let f = cfun id foo in f Nothing
Wrapper False

But regular application (or just (cfun id foo) Nothing) returns the following error:

*Main> cfun id foo $ Nothing
<interactive>:6:1:
    No instance for (Resolution (Maybe a0 -> Wrapper Bool))
      (maybe you haven't applied enough arguments to a function?)
      arising from a use of ‘cfun’
    In the expression: cfun id foo
    In the expression: cfun id foo $ Nothing
    In an equation for ‘it’: it = cfun id foo $ Nothing

In case it helps, the purpose of this code is for cfun to have the effective type of

cfun :: (Eq a0, Eq a1, .., Eq an) => (Wrapped b -> Wrapped c) 
     -> (Maybe a0 -> Maybe a1 -> .. -> Maybe an -> Wrapped b) 
     -> (Maybe a0 -> Maybe a1 -> .. -> Maybe an -> Wrapped c)

i.e. apply a function to the "wrapped" return value of another function of the above form.

Tested on GHC 8.0.1-rc2 (most recent OSX binary as of now) and 7.10.3.

Trac metadata

Trac field	Value
Version	8.0.1-rc2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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