为什么收到的电子邮件不会显示在Thunderbird中？

环境：Ubuntu 14.04 / 14.10上的Thunderbird 31.4.0

症状：收到了来自Yahoo Mail的电子邮件，但是没有出现在预览中，并且在双击打开一个新选项卡时也没有出现。

示例：电子邮件到达。它显示在“收件箱”中，并在表中以粗体显示，表示未读。单击该行不会更改读取状态。它仍然标记为未读。预览窗格如下所示：

双击该行也不会更改读取状态，并且打开的“对话阅读器”选项卡如下所示：

Right-clicking on the line and choosing Mark > As Read will mark it as read, though this does not affect my ability to read the messages.

What Is Unaffected:

• My RSS feeds behave normally
• Calendar behaves normally
• Print Preview of an email message works, so the email bodies are definitely being downloaded.

When This Happened: It started about two weeks ago. I seem to recall getting an Thunderbird update, which would have been to 31.4.0, right before this started.

Attempts at Mitigation:

• I have upgraded Ubuntu to 14.10, with no effect
• I have moved my ~/.thunderbird directory to a temporary location, uninstalled Thunderbird, reinstalled Thunderbird, and moved my original ~/.thunderbird directory back to its original location, with no effect
• 我遵循了“重建全局数据库”的指示，但没有任何效果。

关于如何使Thunderbird允许我再次阅读电子邮件的任何建议？