@Terabyte Thank you for the reply. Repair didn't work, but it got me on the right track.
Basically I have to reinstall CUE every time I reboot or start the computer. Then the side buttons work fine.
Reason I didn't see this effect when I reinstalled previously, is that my usual practice is to reboot after I install any software, which in this case is futile.
I messaged Henry for access to the beta version of CUE, cause I really would like to avoid the constant reinstall and reconfigure routine. :D