Arrrr well… Yes, but no…
Velbus is a self contained protocol, where devices place status updates onto its bus, for other modules to react to.
The basics are…
A button is pressed - device sends a packet saying “device ID, Button number, status” in this case is “PRESSED”
A button is held - device sends a packet saying “device ID, Button number, status” in this case is “LONG_PRESS”
A button is released - device sends a packet saying “device ID, Button number, status” in this case is “RELEASED”
A module that is programmed to respond to an event will activate, also putting a status update on the bus device sends a packet saying “device ID, Channel number, status” in this case is “ON”
However…
The glass panels can do SO much more than just be a Single / Double / Quad button device.
Herman could have programmed a two button panel with multiple button actions.
For example…
1 quick pressed of button 1 will send packets stating that Button 1 has been pressed & released.
But a 2nd press of that same button will send packets saying that a virtual button has been pressed and released. (Thus causing a different set of events)
3rd press of that same button will send packets saying that a 2nd virtual button has been pressed and released.
Or…
Buttons can be put into DUAL mode.
Meaning that a short press of a button will send packets saying that the button has been pressed and released
A LONG press of that same button will send packets saying that a virtual / second button has been pressed and released (but not send a status packet about the primary / physical button)
Alternatively…
He could have programmed a relay to respond to LONG_PRESS packets only, which would mean a button must be pressed & held before an output module responds.
Lamp A responds to Pressed
Lamp B responds to Long_Pressed
However, none of that infomation accounts for why it works within the confines of Velbus, but directly switching the state of the output channel from OpenHab2 (in this case a relay) causes 2 relays to react. (This is not behaviour I have seen before)
OpenHab2 merely instructs to perform an action.
In this case I am assuming that Herman has created a number of OpenHab2 Switches to directly control the output relays.
(The feedback LEDs on the Velbus panels will show the new state of their linked outputs, regardless of how their state was changed)
FYI @cedricboon has added trigger channels so that OpenHab2 rules can respond to the 3 button states.