[APP] ROBB smarrt Z-wave and Zigbee app

I am trying to get the most out of these wall switches by assigning different actions to the different types of button presses in advanced flows. As marked up in the screenshot (in Dutch) the long press ON (Dimming UP) works, but the long press OFF (Dimming DOWN) does not. I am wondering whether this is by design, a bug in the app, or a faulty device. Hope anybody can help. I also messaged RobbShop directly but no satisfactory answer yet.