In the key buttons menu, I can't click on the EX1, 2, 3, and 4 buttons in order to change their keys. Of particular annoyance is that my usual configuration includes some of those button's defaults, leading to the "key bindings must be unique" message. I was eventually able to set them by tabbing onto them and pressing enter, quickly followed by the key I wanted to set it as.
If you don't press the desired key quickly enough (and this could be another bug, as it goes for setting all buttons), enter gets set as your chosen key for that button.