confused about conn.is_connected()(a bug ?)

[YueHonghui]

when is_connected() return True, is it said that the connection is established with mysql? In my case, before every conn.query(), I will call ensure_connected() which to check is_connected() is True(will do reconnect if False).But a Exception complain about "Broken Pipe" throwed when I call conn.query(sql).