通过UWP EmailManager发送电子邮件附件不起作用

使用以下代码从通用应用程序发送附件无效，为什么？

        Dim emailMessage As New EmailMessage()
        emailMessage.[To].Add(New EmailRecipient("[email protected]"))
        emailMessage.Subject = "Test"
        emailMessage.Body = "Hello World"

        Dim localAppFolder = Windows.Storage.ApplicationData.Current.LocalFolder
        Dim file = Await localAppFolder.CreateFileAsync("SomeFile.txt", Windows.Storage.CreationCollisionOption.ReplaceExisting)
        Await Windows.Storage.FileIO.WriteTextAsync(file, "aaaa")
        Dim fileRef = RandomAccessStreamReference.CreateFromFile(file)
        emailMessage.Attachments.Add(New EmailAttachment(file.Name, fileRef))
        Await EmailManager.ShowComposeNewEmailAsync(emailMessage)

收件人，主题和正文在Outlook中显示正常，但缺少附件：Outlook屏幕快照