I think it would be nice to have PR #881 on this beta. The behavior of joystick buttons on LWJGL3 is different of how it used to be on LWJGL2. #881 fixes it.
More about the issue here: [SOLVED] ActionListener: onAction called for no reason - #8 by Pesegato
By the way, it is not solved (I don’t think it’s solved until it’s fixed on the official jME).