Github user StephanEwen commented on the issue:
https://github.com/apache/flink/pull/4900
I think that `quiesce()` should be called before `close()` is called on the
operator, so that after `close()` no new timers can fire. That was the main
purpose of the original change, because after close(), the operator may not be
able to handle firing timers any more.---
