producer.q log printing sending msgs after instructing it to stop

Running q producer.q, I type '\t 100'.
It prints sending a msg every few ms.
After a while, I type '\t 0' to stop. When I do that, it seems to suddenly prints a big batch of msgs  - but using a client at the same time those batch of msgs are never received. Not sure if there were actually sent, since they seem to be printed after doing the cmd to stop the sends. 