Type inference breaking change in GHC 8.0.2

A regression reported by Milewski,

{-# LANGUAGE RankNTypes #-}
module Test where
  
import Data.Profunctor
  
proj :: Profunctor p => forall c. (forall a. p a a) -> p c c
proj e = e

f1 :: Profunctor p => (a -> b) -> (forall c. p c c) -> p a b 
f1 f e = dimap f id (proj e)

Where these definitions no longer type check

-- • Couldn't match type ‘p c0 c0’ with ‘forall a1. p a1 a1’
--   Expected type: p c0 c0 -> p a a
--     Actual type: (forall a1. p a1 a1) -> p a a
-- • In the second argument of ‘(.)’, namely ‘proj’
--   In the expression: dimap id f . proj
--   In an equation for ‘f2’: f2 f = dimap id f . proj
-- • Relevant bindings include
--     f2 :: (a -> b) -> (forall c. p c c) -> p a b
--       (bound at 24:1)
f2 :: Profunctor p => (a -> b) -> (forall c. p c c) -> p a b 
f2 f = dimap id f . proj

-- • Cannot instantiate unification variable ‘a0’
--   with a type involving foralls: (forall c. p c c) -> p a b
--     GHC doesn't yet support impredicative polymorphism
-- • In the expression: undefined
--   In an equation for ‘f3’: f3 f = undefined
-- • Relevant bindings include
--     f :: a -> b
--       (bound at 39:4)
--     f3 :: (a -> b) -> (forall c. p c c) -> p a b
--       (bound at 39:1)

f3 :: Profunctor p => (a -> b) -> (forall c. p c c) -> p a b 
f3 f = undefined -- dimap id f . proj