Very odd. Works just fine here. Be aware that this may not work if a game controls the gamepad! vorpX has to have control of the gamepad.
You cannot use a game’s internal gamepad handling and the vorpX gamepad emulation at the same time. In such a case you have to disable the gamepad in the game for vorpX to take over first.
When the vorpX gamepad emulation is active, all you have to do is clicking the according button on the gamepad page of the ingame menu (which then displays “…”) and afterwards push the according button on the gamepad.