Type inference error while pattern matching

Question

In the below code I keep getting this error — pattern type is incompatible with expected type; Which I feel is incorrect. Is this a possible bug in Scala 2? Anywhere I can read more about it?

    sealed trait Foo[A] { self =>
      def eval: Option[A] =
        self match {
          case Foo.Number => Option(1)
          case Foo.Text   => Option("Ok")
        }
    }
    
    object Foo {
      case object Number extends Foo[Int]
      case object Text extends Foo[String]
    }
    
    println("ok!")

Weirdly it works when eval is implemented in the companion object Foo