TFS WorkItem附件可以保存，但不能加载

Question

我可以将附件保存到WorkItem，如下所示：

TfsTeamProjectCollection tfsTeamProjects = new TfsTeamProjectCollection(new Uri(tfsServerUrl));
WorkItemStore tfsWorkItemStore = tfsTeamProjects.GetService<WorkItemStore>();
WorkItem tfsWorkItem = tfsWorkItemStore.GetWorkItem(tfsWorkItemId);

FileInfo fi = new FileInfo(@"D:\\Docs\testfile.txt");
Attachment tfsAttachment = new Attachment(fi.FullName);
tfsWorkItem.Attachments.Add(tfsAttachment);
tfsWorkItem.Save();

但是当我尝试获取WorkItem的附件列表时，如下所示：

TfsTeamProjectCollection tfsTeamProjects = new TfsTeamProjectCollection(new Uri(tfsServerUrl));
WorkItemStore tfsWorkItemStore = tfsTeamProjects.GetService<WorkItemStore>();
WorkItem tfsWorkItem = tfsWorkItemStore.GetWorkItem(tfsWorkItemId);
foreach(Attachment tfsAttachment : tfsWorkItem.Attachments)
{
    // Do things here
}

tfsWorkItem.Attachments总是空的，即使我可以在TFS上的Objects选项卡中看到四个附件。我得到的WorkItem对象是正确的。