FULL PRODUCT VERSION :
java version "9-ea"
Java(TM) SE Runtime Environment (build 9-ea+159)
Java HotSpot(TM) 64-Bit Server VM (build 9-ea+159, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Windows 7 x64 [6.1.7601]

A DESCRIPTION OF THE PROBLEM :
The provided source code fails to compile due to method overload ambiguity over "fx.method(new FxSubscriber<T>() {":

The pattern compiles fine with Java 8u121 with target -6.

IntelliJ also doesn't indicates any ambiguity in its editor window (Build #IU-171.3691.12, built on March 1, 2017).


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Compile the supplied code with javac target -9

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Compiles fine
ACTUAL -
Compilation error

ERROR MESSAGES/STACK TRACES THAT OCCUR :
Error:(15, 11) java: reference to method is ambiguous
  both method method(java.util.concurrent.Flow.Subscriber<? super T>) in hu.akarnokd.java9.benchmark.OverloadResolution.Fx and method method(hu.akarnokd.java9.benchmark.OverloadResolution.FxSubscriber<? super T>) in hu.akarnokd.java9.benchmark.OverloadResolution.Fx match

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.util.concurrent.Flow;

public class OverloadResolution {

    interface FxSubscriber<T> extends Flow.Subscriber<T> { }

    abstract class Fx<T> {
        void method(Flow.Subscriber<? super T> f) { }
        void method(FxSubscriber<? super T> f) { }
    }

    <T> void m() {
        Fx<? extends T> fx = new Fx<T>() { };

        fx.method(new FxSubscriber<T>() {
            @Override
            public void onSubscribe(Flow.Subscription subscription) {

            }

            @Override
            public void onNext(T item) {

            }

            @Override
            public void onError(Throwable throwable) {

            }

            @Override
            public void onComplete() {

            }
        });
    }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Change Fx<? extends T> into Fx<T> (may require suppressing the