The issue turned up in working on JDK-8244531. Failing test case:

    @Test
    public void testButtonBehaviorMemoryLeak() {
        Button control = new Button();
        WeakReference<BehaviorBase<?>> weakRef = new WeakReference<>(createBehavior(control));
        assertNotNull(weakRef.get());
        weakRef.get().dispose();
        attemptGC(weakRef);
        assertNull("behavior must be gc'ed", weakRef.get());
    }
    
Problem missing removal of listener to control's focusedProperty. Actually, the behavior tries to but gets it wrong:

     // in constructor
     getNode().focusedProperty().addListener(this::focusChanged);

    // in dispose
    getNode().focusedProperty().removeListener(this::focusChanged);

the incorrect assumption here is that the lambda being remove is the _same_ instance as the one added (which isn't the case)

Fix is to have a field for the focusListener and add/remove that

    InvalidationListener listener = this::focusChanged;
    ...
     // in constructor
     getNode().focusedProperty().addListener(focusListener);

    // in dispose
    getNode().focusedProperty().removeListener(focusListener);

Same issue with same reason and fix in ComboBoxBaseBehavior - will defer fix until JDK-8244531 is integrated (can then add cross-behavior test)