OH2 is sending 2 mqtt messages every time you press the Robo500 button on your sitemap?
Most likely, you followed the tutorial on the first post, setup your MQTT-Event Bus config in a previous step and later on, you commented out the stuff in /etc/openhab2/services/mqtt-eventbus.cfg.
This does not make the parameters go away from their storage destination = /var/lib/openhab2/config/org/openhab/mqtt-eventbus.config (there is an issue with stale configs).
To make them go away, you should not comment them out but set them to nothing, or use the config pid: story as the first line in your *.cfg
This means that the Item will trigger one MQTT message from the “focused” binding config and another MQTT message will be initiated from the EventBus integration = resulting in 2 messages (@rlkoshak it seems that this works as expected 
)
Can you check and post the contents of /var/lib/openhab2/config/org/openhab/mqtt-eventbus.config ?
If there is something there: stop OH2, delete this file, start OH2.
99,9% this is the problem… but you never know… so post also your sitemap config plz just to check it