Czemu tak jest? Program java

Question

Witam! Otóż mam taki kod:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;
import java.io.*;


public class TaskKiller extends JFrame implements ActionListener {
	JButton exitBtn, minimizeBtn, maximizeBtn, OkExitBtn;
	JFrame frame, minimizedFrame, err;
	
	public static void main(String[] args)
	{
		String task = null; 
		Scanner scan = new Scanner(System.in);
		new TaskKiller();
		
	}
	
	public TaskKiller()
	{
		Dimension dim = Toolkit.getDefaultToolkit().getScreenSize();
		double xFrame = dim.getWidth() - 455;
		double yFrame = dim.getHeight() - 225;
		double xMFrame = dim.getWidth() - 50;
		double yMFrame = dim.getHeight() - 100;
		
		minimizedFrame = new JFrame();
		minimizedFrame.setUndecorated(true);
		minimizedFrame.setVisible(false);
		minimizedFrame.setBounds((int)xMFrame,(int)yMFrame, 50,50);
		minimizedFrame.setResizable(false);
		minimizedFrame.setAlwaysOnTop(true);
		
		
		frame = new JFrame("TaskKiller");
		frame.setResizable(false);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setBounds((int)xFrame,(int)yFrame,450,175);
		frame.setUndecorated(true);
		frame.setVisible(true);
		frame.setAlwaysOnTop(true);
		frame.setBackground(Color.black);
		
		err = new JFrame("Error");
		err.setVisible(false);
		err.setResizable(false);
		err.setLocationRelativeTo(null);
		err.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		err.setSize(500,500);
		
		
		minimizeBtn = new JButton();
		minimizeBtn.setBounds(390, 0, 30, 30);
		minimizeBtn.setBackground(Color.blue);
		minimizeBtn.addActionListener(this);
		
		maximizeBtn = new JButton();
		maximizeBtn.setBounds(0,0,0,0);
		maximizeBtn.setBackground(Color.blue);
		maximizeBtn.addActionListener(this);
		
		
		exitBtn = new JButton();
		exitBtn.setBounds(420, 0, 30,30);
		exitBtn.setBackground(Color.red);	
		exitBtn.addActionListener(this);

		OkExitBtn = new JButton();
		OkExitBtn.setBounds(220, 450, 30,50);	
		OkExitBtn.addActionListener(this);
		
		
		frame.add(exitBtn);
		frame.add(minimizeBtn);
		minimizedFrame.add(maximizeBtn);

	}
	public void actionPerformed(ActionEvent e) {
		Object source = e.getSource();
		
		if(source==exitBtn||source==OkExitBtn)
		{
			err.dispose();
			minimizedFrame.dispose();
			frame.dispose();
		}
		else if(source==minimizeBtn)
		{
			frame.setVisible(false);
			minimizedFrame.setVisible(true);
		}
		else if(source==maximizeBtn)
		{
			minimizedFrame.setVisible(false);
			frame.setVisible(true);
			minimizeBtn.setBounds(390, 0, 30, 30);
			minimizeBtn.setSize(30,30);
		}
		else
		{
			err.setVisible(true);
		}
	}
	
}

I co jakiś czas, gdy uruchamiam program, przycisk "minimizeBtn", zakrywa całą dostępną przestrzeń, zamiast tylko swoje 30x30 px w rogu... Co może to powodować? Da się temu zaradzić? Prosiłbym o pomoc...