Platform: All
JDK: 1.4+
class: java.awt.Toolkit
method: http://download.java.net/jdk7/docs/api/java/awt/Toolkit.html#getPropertyChangeListeners()

    --------------------------------------------------------------------------------
    public PropertyChangeListener[] getPropertyChangeListeners()
    Returns an array of all the property change listeners registered on this toolkit.
    Returns:
          all of this toolkit's PropertyChangeListeners or an empty array
          if no property change listeners are currently registered
    --------------------------------------------------------------------------------

 Assertion above is not correct.
 In fact method returns proxies, not listeners.

 Please see the following code sample for illustration:

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import java.awt.*;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.util.Arrays;

public class Test {
    public static void main(String[] args) {

        // this is for shortness, this behavior exist in default methods of Toolkit class
        // so any stubbed Toolkit child could be used as well
        Toolkit toolkit = Toolkit.getDefaultToolkit();

        toolkit.addPropertyChangeListener("prop", new PropertyChangeListener() {
            @Override public void propertyChange(PropertyChangeEvent evt) { }
            @Override public String toString() { return "my pcl"; }
        });

        PropertyChangeListener[] byProp = toolkit.getPropertyChangeListeners("prop");
        PropertyChangeListener[] all = toolkit.getPropertyChangeListeners();

        System.out.println("getPropertyChangeListeners(\"prop\") = " + Arrays.toString(byProp));
        System.out.println("getPropertyChangeListeners() = " + Arrays.toString(all));
    }
}
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The output will look like

getPropertyChangeListeners("prop") = [my pcl]
getPropertyChangeListeners() = [java.beans.PropertyChangeListenerProxy@17ec251]