zookeeper shows two leaders after election

Hi

We are using zookeeper 3.3.4 in our production cluster with 5 machines with
additional 4 observers for read traffic. We currently observe some weird
behavior when zookeeper relects leader to another server, sometimes, the
old zookeeper seems still in the state of LEADING (even though it
disconnects the other followers) and new leader has been elected. We could
still see the following log message after the server loses leadership. And
it causes observer to continuously connect to the server. The session
timeout for observer is set to 1 hour. (I'm not sure if it's relevant here
though)

INFO [WorkerReceiver Thread:FastLeaderElection [ at ] 496] - Notification: 5
(n.leader), 1988571642783 (n.zxid), 535 (n.round), LEADING (n.state), 5
(n.sid), LEADING (my state)

Do you guys know any bugs for zookeeper 3.3.4 that could have this issue or
how shall we debug this issue further ?

Thanks a lot,

Weide