phpmqtt_input script blocking publish to MQTT

Maybe it's me but I'm finding that inputs received from the phpmqtt_input script cannot then be published back to a different topic via Publish to MQTT. I assume the port is still blocked by the script receiving but without any error messages I'm just guessing. I'm very much an MQTT novice but I thought there was a guaranteed delivery mechanism or is it that the basic PHP implementation doesn't have this ?

Inputs received via the RFM12PI and HTTP API will publish just fine.

Using the emoncms extended (9 RC2 | 2015.09.15) on a RaspberryPi2 running from a USB HDD