Unable to use functional interface as a SAM because of Scala's "concrete beats deferred" rule

[retronym]

package p1;

public class Test {
    @FunctionalInterface
    public static interface A {
        String foo();
    }
    @FunctionalInterface
    public static interface B extends A {
        default String bar() { return bar(); };
        String foo();
    }
    @FunctionalInterface
    public static interface C extends B {
        @Override String bar();
        default String foo() { return "C"; }
    }
}

scala> println(samOf(typeOf[p1.Test.C]))
<none>

It isn't clear to me that the current approach of treating Java default methods as concrete from the perspective of the Scala type system is the right approach. (We already have a different mechanism to mark them: Flag.JAVA_DEFAULT_METHOD), which we can use in override checks, etc.