根据 Henrik Nordstrom 的邮件发现的squid2.6现行版本中存在几个问题：
1. object with ETag but not Vary cached.
2. plain GET request received after the object had expired.
3. The request forwarded to the server had If-Modified-Since, but no If-None-Match.
其中第二个是一个比较严重的bug，把过期的内容返回给用户。至于第一和第三个问题，仍然是需要去模拟重现出问题，才好跟踪原因。
