What The Hell Scala?

WTH.scala

case class Cont[F[+_], +A] extends Free[F, A] 
sealed trait Free[F[+_], +A]

case class FreeM[I, +A](free: Free[({type f[+x] = Map[I, x]})#f, A]) {
  def run = {  
    free match {
      case Cont() =>
        error("")        
    }
  }
}

/*
$ scalac X.scala 
WTH.scala:7: error: constructor cannot be instantiated to expected type;
 found   : Cont[F,A(in class Cont)]
 required: Free[[+x]scala.collection.immutable.Map[I,x],A(in class FreeM)]
      case Cont(e) =>
           ^
one error found
*/

// more reduced
sealed trait Foo[F[+_]]
case class Bar[F[+_]]() extends Foo[F]

def works[F[+_]](f: Foo[F]) {
  f match {
    case Bar() => ???
  }
}

def fails[I](f: Foo[({type F[+x] = Map[I, x]})#F]) {
  f match {
    case Bar() => ???
  }
}

https://issues.scala-lang.org/browse/SI-6744 ?