App.java:
public class App extends Application {
    @Override
    public void start(Stage stage) {
        stage.setScene(new Scene(new TextArea("01234\n56789\n")));
        stage.show();
    }
}
To reproduce:
1. Run the above code
2. Do a single mouse click anywhere below the second line of text ("56789")
3. Cursor is appearing at the end of line 2 (after '9'). Cursor is expected on line 3
4. Push down keyboard button. Cursor does not move to line 3. Cursor is expected to move to line 3
5. Push up button, then push down button two times. Cursor is now on line 3