The CalendarTextField control reuses the fairly spacious CalendarPicker control; the picker is shown in a popup window below the textfield when an icon new to the textfield is clicked. In my testcase (CalendarTextFieldText1 in JFXtras) the popup window happens to partly overlap the JavaFX window and partly fall outside (see attachement). As soon as the popup window is visible and the mouse is moved over any control inside the popup (label or togglebutton), the part overlapping the JavaFX window blinks with every mouse event (or so it appears).