I meant that the click event is basically copying the command from the click event in the players chat and sending it immediately. That's why click events also have the same restrictions as the player chat ^^.
Edit: That's also the reason why people need op to use most of the click events ^^ (or a trigger)
Ah, I didn't know that. I thought it would trigger the command block again instead of the player chat, but now that I think about it that makes no sense.