KStream window - end value out of bounds

[Jon Yeargers]

Using the following topology:

KStream<String,SumRecord> kStream =
 kStreamBuilder.stream(stringSerde,transSerde,TOPIC);
        KTable<Windowed<String>, SumRecordCollector> ktAgg =
kStream.groupByKey().aggregate(
                SumRecordCollector::new,
                new Aggregate(),
                TimeWindows.of(20 * 60 * 1000).advanceBy(60 * 1000),
                cSerde, "table_stream");


When looking at windows as follows:

           ktAgg.toStream().foreach((postKey, postValue) -> {
                 LOGGER.debug("start: {}   end: {}",
postkey.window().start(), postkey.window().end());
           }

The 'start' values are coming through properly incremented but the 'end'
values are all 9223372036854775807.

Is there something wrong with my topology? Some other bug that would cause
this?