ZipFile.CreateFromDirectory追加带有双扩展名的压缩文件夹

Question

我正在考虑这可能是一个错误。我的方法创建一个zip文件，似乎正确地写入文件和文件夹。一旦我通过catch块，它就会遇到FileNotFound异常，并且在检查.zip时，它会以下列格式附加文件：
[filename].zip.zip

我有什么问题吗？

private void compressDirectory()
{
    zipPath = backupPath + @"\" + DateTime.Now.ToString("yyyy-MM-dd-HH-mm") + ".zip";
//At this point, zipPath has the value "c:\testfacility\tree\<date+time>" 
                                                   //which definitively exists.
    try
    {
        ZipFile.CreateFromDirectory(sourcePath, zipPath, CompressionLevel.Optimal, true);
        getresultmessage(); //this line is never hit
    }
    catch (IOException v)
    {
        errMsg = "Failed trying to start compression. \n" + v.ToString();
    }
}