GridBagLayout Pixel Offset from Anchor Position

Question

How do I remove the pixel offset from the SW-Button corner?

Some sizes will work, while others won't I'm just looking for a reliable way to always have the button be in the very bottom-right corner.

I've tried different values for weightx/y and ipadx/y which fix it for specific sizes but just create the issue again on others.

Is this just a general problem with GridBagLayout or am I missing something?

import java.awt.Color;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import javax.swing.JButton;
import javax.swing.JFrame;

public class TestFrame extends JFrame {

    public static void main(String[] args) {
        new TestFrame();
    }

    public TestFrame() {
        this.setDefaultCloseOperation(EXIT_ON_CLOSE);
        this.setSize(501, 500);
        this.getContentPane().setBackground(Color.MAGENTA);
        
        this.setLayout(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();
        
        gbc.fill = GridBagConstraints.NONE;
        gbc.weightx = 1;
        gbc.weighty = 1;
        
        gbc.gridx = 0;
        gbc.gridy = 0;
        gbc.anchor = GridBagConstraints.NORTHWEST;
        
        JButton nw = new JButton("NW");
        this.add(nw, gbc);
        
        gbc.gridx = 1;
        gbc.gridy = 1;
        gbc.anchor = GridBagConstraints.SOUTHEAST;
        
        JButton se = new JButton("SW");
        this.add(se, gbc);
        
        this.setVisible(true);
    }
}