Unexpected KStream-KStream join behavior with asymmetric time window

[Elias Levy]

Using Kafka 0.10.0.1, I am joining records in two streams separated by some
time, but only when records from one stream are newer than records from the
other.

I.e. I am doing:

  stream1.join(stream2, valueJoiner, JoinWindows.of("X").after(10000))

I would expect that the following would be equivalent:

  stream2.join(stream1, valueJoiner, JoinWindows.of("X").before(10000))

Alas, I find that this is not the case.  To generate the same output as the
first example I must do:

  stream2.join(stream1, valueJoiner, JoinWindows.of("X").after(10000))

What am I missing?