如何正确处理PrivateFontCollection

我正在使用PrivateFontCollection在我的web服务器上安装上传的字体。下面的代码可以工作，但在第二次上传字体时，PrivateFontCollection会引用上传的第一个字体。所以有些东西没有得到正确的处理。有人发现我做错了什么吗？

 var fontName = string.Empty;
    using (var ms = new MemoryStream(fontBytes))
    {
        // used to store our font and make it available in our app
        using (var pfc = new PrivateFontCollection())
        {
            //create memory pointer
            IntPtr data = Marshal.AllocCoTaskMem((int)ms.Length);
            try
            {
                //copy the bytes to the unsafe memory block
                Marshal.Copy(fontBytes, 0, data, (int)ms.Length);
                // We HAVE to do this to register the font to the system (Weird .NET bug !)
                uint cFonts = 0;
                AddFontMemResourceEx(data, (uint)fontBytes.Length, IntPtr.Zero, ref cFonts);
                //pass the font to the font collection
                pfc.AddMemoryFont(data, (int)ms.Length);
                var fontWithMime = "data:application/x-font-truetype;charset=utf-8;base64," + cleanFontData;
                fontName = pfc.Families[0].Name;
                //db work here
            }
            finally
            {
                ms.Close();
                Marshal.FreeCoTaskMem(data);
            }
        }
    }