关于Image.FromStream()变换图片产生的问题

最近学习C#编程，想自己编些桌面小程序玩玩，接触到了线程，GDI+，网络文件传输一系列的东东。编这些程序前我已经知道这水很深，可是接触了，才发现这水这么这么深，会淹死人的……几乎每天都是从早到晚的盯着MSDN，这个连接跳到那个连接，那个连接又跳回这个连接，那个寒啊……

言归正传，在编程的时候发现了一个问题，关于绘制Image.FromStream()所产生的图片时候会出现内存不足的警告。而Image.FromFile()着根本不会出现这问题，实在是很不解啊。

现将代码公布如下，给大家参考，希望大家可以告诉我，这是为什么。。。难道这就是传说中的BUG~~我运气也太好了点呀。。。。微软是不是要发点奖金给我。。呵呵。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Drawing.Drawing2D;
using System.IO;

namespace Project1
{
    public partial class Clock : Form
    {
        //定义一个Image
        Image image1;
        //旋转角度,值为90和180的时候绘制会产生内存不足警告
        float float1 = 88;

        //定义128*128图象的初始点
        Point[] PT = new Point[] { new Point(-64, -64), new Point(64, -64), new Point(-64, 64) };

        public Clock()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            this.Refresh();
            float1++;
            label1.Text = float1.ToString();
            System.Drawing.Graphics PicGraphics = this.pictureBox1.CreateGraphics();
            //把64，64点设置为中心点，将以这个中心点为圆心旋转
            PicGraphics.TranslateTransform(64, 64);
            GraphicsState gs = PicGraphics.Save();
            PicGraphics.RotateTransform(float1);
            PicGraphics.DrawImage(image1, PT);
            PicGraphics.Restore(gs);
            PicGraphics.Dispose();
        }

        private void Clock_Load(object sender, EventArgs e)
        {
            label1.Text = float1.ToString();

            //读取一个128*128的PNG文件
            byte[] nbytes = new byte[(new FileInfo("a.png")).Length];
            using (FileStream fs = new FileStream("a.png", FileMode.Open, FileAccess.Read, FileShare.Read, 1, true))
            {
                fs.Read(nbytes, 0, nbytes.Length);
                using (Stream stream = new MemoryStream(nbytes))
                {
                    image1 = Image.FromStream(stream);

                }
            }

        }

        private System.Windows.Forms.Button button1;
        private System.Windows.Forms.PictureBox pictureBox1;
        private System.Windows.Forms.Label label1;

        private void InitializeComponent()
        {
            this.button1 = new System.Windows.Forms.Button();
            this.pictureBox1 = new System.Windows.Forms.PictureBox();
            this.label1 = new System.Windows.Forms.Label();
            ((System.ComponentModel.ISupportInitialize)(this.pictureBox1)).BeginInit();
            this.SuspendLayout();
            // 
            // button1
            // 
            this.button1.Location = new System.Drawing.Point(12, 12);
            this.button1.Name = "button1";
            this.button1.Size = new System.Drawing.Size(75, 23);
            this.button1.TabIndex = 0;
            this.button1.Text = "增加1角度";
            this.button1.UseVisualStyleBackColor = true;
            this.button1.Click += new System.EventHandler(this.button1_Click);
            // 
            // pictureBox1
            // 
            this.pictureBox1.Location = new System.Drawing.Point(73, 65);
            this.pictureBox1.Name = "pictureBox1";
            this.pictureBox1.Size = new System.Drawing.Size(128, 128);
            this.pictureBox1.TabIndex = 1;
            this.pictureBox1.TabStop = false;
            // 
            // label1
            // 
            this.label1.AutoSize = true;
            this.label1.Location = new System.Drawing.Point(125, 22);
            this.label1.Name = "label1";
            this.label1.Size = new System.Drawing.Size(17, 12);
            this.label1.TabIndex = 2;
            
            // 
            // Clock
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 12F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(292, 266);
            this.Controls.Add(this.label1);
            this.Controls.Add(this.pictureBox1);
            this.Controls.Add(this.button1);
            this.Name = "Clock";
            this.Text = "Clock";
            this.Load += new System.EventHandler(this.Clock_Load);
            ((System.ComponentModel.ISupportInitialize)(this.pictureBox1)).EndInit();
            this.ResumeLayout(false);
            this.PerformLayout();

        }

        static class Program
        {
            /**//// <summary>
            /// 应用程序的主入口点。
            /// </summary>
            [STAThread]
            static void Main()
            {
                Application.EnableVisualStyles();
                Application.SetCompatibleTextRenderingDefault(false);
                Application.Run(new Clock());
            }
        }

    }
}