C# foreach iteration

Good day all,

I am not the worlds most experienced C# developer so please bear with me :)
Recently started to move projects over to .NET C#.

I have a very simple issue which I do not seem to understand.

I have a method that creates buttons and also another method that disposes them off.
But in the disposing method my foreach iteration seems to miss the last control everytime.

I am not sure as to why this would happen.
Two buttons gets created in dynamically no problem.
When running the DisposeButtons() method all except one button gets removed.

Please see my code - been on loooong day so perhaps I am overlooking something here.

Thanks in advance :)

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            LoadButtons();
        }

        private void LoadButtons()
        {
            var top = 20;
            var verticalspace = 5;

            for (int x = 0; x < 2; x++)
            {
                top += top + verticalspace;

                Button b = new Button();
                b.Text = "button_" + x.ToString();
                b.Top = top;
                b.Left = 20;
                b.Name = "button_" + x.ToString();
                this.Controls.Add(b);
            }
        }

        private void DisposeButtons()
        {
            foreach (Control c in this.Controls)
            {
                if (c is Button) {
                    this.Controls.Remove(c);
                }
            }
        }

        private void checkBox1_CheckedChanged(object sender, EventArgs e)
        {
            if (checkBox1.Checked)
            {
                LoadButtons();
            }
            else
            {
                DisposeButtons();
            }
        }
    }
}

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