MQTT command does trigger the ICON but not the action

[lumjajo]

Hello everybody,
I need some help on MQTT.
I can publish an MQTT command, something like:
mosquitto_pub -h 192.168.xxxx -t "domoticz/in" -m '{ "idx" : 28, "nvalue" : 1 }'

Now what happens is, that the respective ICON in domoticz lights up as if switched on, also the domoticz/out messages show the switch is triggered to 1, BUT nothing happens. Means the respective light which should be triggered stays like before, nothing happens.
When i trigger the switch by clicking on the symbol, it works.
Anything I have overseen?
Thanks