Watermarking in Src and Timestamping downstream

[Roshan Naik]

Have streaming use cases where it is useful & easier to generate the watermark 
in the Source (via ctx.emitWatermark() ) and assign timestamps in a downstream 
custom operator which calls  output.collect(new StreamRecord<T>(msg, time)).
When doing so, I see that the watermark reaches the downstream operator, but 
does not flow past it and consequently further downstream windows remain open. 
(I am using Flink 1.6). 
-roshan