Github user StephanEwen commented on the pull request:
https://github.com/apache/flink/pull/1289#issuecomment-150837902
Okay, figured out that the cause of the problem was: The test UDF calls
(evaluated in the processing time timer) emits elements before updating the
state. The test driver already received all elements and checks the state
before it is updated. Switching the statements seems to fix the instability...
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