Scala 2.9.x bug

gistfile1.scala

// With -Ydependent-method-types
// Compiles with 2.10.x

scala> trait Algebra[F[_]] { trait Expr[A] }
defined trait Algebra

scala> trait ClosedExpr { def apply[F[_], A](algebra: Algebra[F]): algebra.Expr[A] }
defined trait ClosedExpr

scala> new ClosedExpr { def apply[F[_], A](algebra: Algebra[F]): algebra.Expr[A] = new algebra.Expr[A] {} }
<console>:10: error: can't existentially abstract over parameterized type F
              new ClosedExpr { def apply[F[_], A](algebra: Algebra[F]): algebra.Expr[A] = new algebra.Expr[A] {} }
              ^

scala> class Foo extends ClosedExpr { def apply[F[_], A](algebra: Algebra[F]): algebra.Expr[A] = new algebra.Expr[A] {} }
<console>:9: error: overriding method apply in trait ClosedExpr of type [F[_], A](algebra: Algebra[F])algebra.Expr[A];
 method apply has incompatible type
       class Foo extends ClosedExpr { def apply[F[_], A](algebra: Algebra[F]): algebra.Expr[A] = new algebra.Expr[A] {} }