Consider:

    class C[+A] {

      private[this] var y: A = _
      def getY: A = y

      class Inner(x: A) {
        y = x
      }
    }

    object Test {

      def main(args: Array[String]) = {
        val x = new C[String]
        val y: C[Any] = x
        val i = new y.Inner(1)
        val s: String = x.getY
        println(s)
      }
    }

This demonstrates an unsoundness in the variance checking of scalac.
Scalac excludes symbols owned by constructors from the
checking. This is unsound, as can be demonstrated by compiling the test
and observing output of the program run:

Exception in thread "main" java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.String
at Test$.main(variances-constr.scala:17)
at Test.main(variances-constr.scala)

Dotty allows this code only under -language:Scala2 and issues a migration warning.