Sliding window without grace not working

Hi everyone! I would like to understand why KafkaStreams DSL offer the ability to express a SlidingWindow with no grace period but seems that it doesn't work. confluent's site state that grace period is required and with the deprecated method, it's default to 24 hours.

Doing a basic sliding window with a count, if I set grace period to 1 ms, expected output is done. Based on the sliding window documentation, lower and upper bounds are inclusive.

If I set grace period to 0 ms, I can see that record is not skipped at KStreamSlidingWindowAggregate(l.126) but when we try to create the window and push the event in KStreamSlidingWindowAggregate#createWindows we call the method updateWindowAndForward(l.417). This method (l.468) check that windowEnd > closeTime.

closeTime is defined as observedStreamTime - window.gracePeriodMs (Sliding window configuration)

windowEnd is defined as inputRecordTimestamp.

For a first event with a record timestamp, we can assume that observedStreamTime is equal to inputRecordTimestamp.

Therefore, closeTime is inputRecordTimestamp - 0 (gracePeriodMS) which results to inputRecordTimestamp.

If we go back to the check done in updateWindowAndForward method, then we have inputRecordTimestamp > inputRecordTimestamp which is always false. The record is then skipped for record's own window.

Stating that lower and upper bounds are inclusive, I would have expected the event to be pushed in the store and forwarded. Hence, the check would be windowEnd >= closeTime.

Is it a bug or is it intended ?

Thanks in advance for your explanations!

Best regards!