The way it's supposed to work is that either button (or both) opens the door, and this is how it usually works for me. I did find a weird bug where if I press both buttons, save and load the game, then get off one button, it closes and I can't get it to open again. But in that case, the door is darkened, not lit like in your screenshot. Maybe it has to do with the delay before it closes and perfect timing for hitting the button? Can you tell me exactly how you caused the issue to occur?
I opened the door using the ball on the first button, stepped on the 2nd button a few times, then rolled the ball away, got my companion to stand on the first button, rolled the ball to the 2nd button, at this point the door was still open. Then I pushed my companion off the button and the door closed and didn't open again when the button was pressed. All of this happened without exiting the room, then I exited and returned and it was still stuck, then I took the screenshot only after I exited and returned a couple of times.