I am having this same problem. New KPLs, same firmware v.43. Must be a bug in the firmware.
Setting a button to non-toggle ON or OFF have the same effect: once the button is pushed, it stays lit forever.
However, in the non-toggle ON mode, ISY recognizes that with the first button push the light comes on and stays lit. In the non-toggle OFF mode, ISY never recognizes that the button comes on - ISY always says the status of the button is OFF.