Option GADTs specialises a polymorphic value in local bindings

This module typechecks WITHOUT the extension GADTs and doesn't typecheck WITH the extension GADTs

Since it has nothing to do with GADTs, the consequence of using the option is surprising.

I witnessed this behaviour on GHC versions 7.6.3, 7.8.3, 7.8.4, 7.10.1

{-# LANGUAGE
     RankNTypes
   , GADTs  
 #-}
module GADTMonomorphism where

problem :: (forall x . () -> x) -> (a,b)
problem f = (p, p)
  where p = f ()

Trac metadata

Trac field	Value
Version	7.10.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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