BugOuterPart1 under 2.10.2.out

$ scalac -unchecked -Xprint:explicitouter,lambdalift,constructors BugOuterPart1.scala
[[syntax trees at end of             explicitouter]] // BugOuterPart1.scala
package <empty> {
  class Outer extends Object {
    def <init>(): Outer = {
      Outer.super.<init>();
      ()
    };
    final class Inner extends Object {
      def <init>($outer: Outer.this.type): Outer.this.Inner = {
        Inner.super.<init>();
        ()
      };
      <synthetic> <paramaccessor> private[this] val $outer: Outer.this.type = _;
      <synthetic> <stable> def Outer$Inner$$$outer(): Outer = Inner.this.$outer
    }
  }
}

[[syntax trees at end of                lambdalift]] // BugOuterPart1.scala
package <empty> {
  class Outer extends Object {
    def <init>(): Outer = {
      Outer.super.<init>();
      ()
    };
    final class Inner extends Object {
      def <init>($outer: Outer): Outer.this.Inner = {
        Inner.super.<init>();
        ()
      };
      <synthetic> <paramaccessor> private[this] val $outer: Outer = _;
      <synthetic> <stable> def Outer$Inner$$$outer(): Outer = Inner.this.$outer
    }
  }
}

[[syntax trees at end of              constructors]] // BugOuterPart1.scala
package <empty> {
  class Outer extends Object {
    final class Inner extends Object {
      def <init>($outer: Outer): Outer.this.Inner = {
        Inner.super.<init>();
        ()
      }
    };
    def <init>(): Outer = {
      Outer.super.<init>();
      ()
    }
  }
}

BugOuterPart1.scala

class Outer {
  final class Inner
}

BugOuterPart2 under 2.10.2.out

$ scalac -unchecked -Xprint:specialize,explicitouter BugOuterPart2.scala
[[syntax trees at end of                specialize]] // BugOuterPart2.scala
package <empty> {
  object Matcher extends Object {
    def <init>(): Matcher.type = {
      Matcher.super.<init>();
      ()
    };
    def matchInner(v: Any, o: Outer): Unit = {
      case <synthetic> val x1: Any = v;
      case5(){
        if (x1.isInstanceOf[o.Inner]().&&((x1.asInstanceOf[o.Inner](): o.Inner).<outer>().eq(o)))
          matchEnd4(())
        else
          case6()
      };
      case6(){
        matchEnd4(throw new MatchError(x1))
      };
      matchEnd4(x: Unit){
        x
      }
    }
  }
}

BugOuterPart2.scala:4: warning: The outer reference in this type test cannot be checked at run time.
      case v2: o.Inner =>
           ^
[[syntax trees at end of             explicitouter]] // BugOuterPart2.scala
package <empty> {
  object Matcher extends Object {
    def <init>(): Matcher.type = {
      Matcher.super.<init>();
      ()
    };
    def matchInner(v: Any, o: Outer): Unit = {
      case <synthetic> val x1: Any = v;
      case5(){
        if (x1.isInstanceOf[o.Inner]().&&(true))
          matchEnd4(())
        else
          case6()
      };
      case6(){
        matchEnd4(throw new MatchError(x1))
      };
      matchEnd4(x: Unit){
        x
      }
    }
  }
}

one warning found

BugOuterPart2.scala

object Matcher {
  def matchInner(v: Any, o: Outer) =
    v match {
      case v2: o.Inner =>
    }
}