Bindings.bindContentBidirectional does not work correctly

FULL PRODUCT VERSION :
java version "1.8.0_45"
Java(TM) SE Runtime Environment (build 1.8.0_45-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.45-b02, mixed mode)


ADDITIONAL OS VERSION INFORMATION :
Bug is OS-indepdendent

A DESCRIPTION OF THE PROBLEM :
When overwriting a value to an ObservableMap, the other map will just delete the key but not update it.


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the testcase.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
{key=val2}


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import javafx.beans.binding.Bindings;
import javafx.collections.FXCollections;
import javafx.collections.ObservableMap;

public class BindContentBidirectionalBug {
public static void main(String[] args) {
ObservableMap<String, Object> m1 = FXCollections.observableHashMap();
ObservableMap<String, Object> m2 = FXCollections.observableHashMap();
Bindings.bindContentBidirectional(m1, m2);
m1.put("key", "val1");
m1.put("key", "val2");
System.out.println(m2);
}
}

---------- END SOURCE ----------