Github user fhueske commented on the issue:
https://github.com/apache/flink/pull/5094
I had a look at `testRowTimeJoinWithCommonBounds2`.
The test processes starts by processing two watermarks for `6000` for the
first and second input. After that three records are added for `6000` (first),
`6000` (second), and `1000` (first). All three records are late because their
timestamp is smaller or equal to the current watermark. Therefore, the join
result should also be late. If all three records would be aligned with the
watermarks, the result should not be late.
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