silverlight中MemoryStream内存释放问题？

C# code

            using (MemoryStream ms = new MemoryStream())            {                using (StreamWriter writer = new StreamWriter(ms))                {                    int count = 1024 * 1024 * 40;                    char[] str = new char[count];                                        while (count-- > 0)                        str[count] = '*';                    writer.Write(str);                    writer.Flush();                }            }

今天测试向MemoryStream中写入大数据，结果发现在silverlight中内存不会被释放，达200多MB，但在asp.net中可以。why？