In Scala 3: Why runtime pattern matching can't work reliably on duck type using JVM reflection?

Considering the following example:

object MatchDuckType {

  trait Sup
  class Sub1() extends Sup {
    def v1: String = "a"
  }

  def example(v: Any) = {

    v match {

      case _: Sup { def v1: String } => println(1)
      case _ => println(2)
    }
  }

  def main(args: Array[String]): Unit = {
    example(Sub1())
    example(1)
  }
}

The compiler gave the following error:

MatchDuckType.scala:16:12: the type test for xxx.MatchDuckType.Sup{v1: String} cannot be checked at runtime

This statement is clearly wrong, as Sup { def v1: String } can be easily checked by Java runtime reflection (by first getting the class of the term, then getting its method signatures). Why does the warning still exist? Is it a bug in compiler?