The cap fix won't affect the button lighting; the cap fixes a transient glitch in the pic->digital pot 3-wire interface; this pot is in the feedback loop for the 60v display PSU.

The PIC (which drives the button LEDs) doesn't seem to have a problem getting commands reliably, generally at least. But yes, the LED stuff was never well tested as it was just a quick hack to use some unused pins on the PIC.

Hugo