Adding a second listener to the Java SimpleMapProperty causes neither one to respond.

import javafx.beans.property.MapProperty;
import javafx.beans.property.SimpleMapProperty;
import javafx.collections.FXCollections;

public final class MapPropertyInitialization {

    public static void main(final String[] args) {
        final MapProperty<String, String> mp =
                new SimpleMapProperty<String, String>(
                        FXCollections.observableHashMap());

        mp.addListener((obv1, ov1, nv1) -> {
            System.out.format("1: mp: %s%n", nv1);
        });
        mp.put("key 1", "object 1");

        mp.addListener((obv2, ov2, nv2) -> {
            System.out.format("2: mp: %s%n", nv2);
        });
        mp.put("key 2", "object 2");
    }
}


Should print:

1: mp: {key1=object1}
1: mp: {key2=object2, key1=object1}
2: mp: {key2=object2, key1=object1}

But only the first line shows up.

Adding an empty MapChangeListener corrects the problem.

mp.addListener(new MapChangeListener<String, String>() {
    @Override
    public void onChanged(Change<? extends String, ? extends String> map) {}
});