I finally got around to finishing the new 32-inputs analog board, and in preparation to attach it I re-programmed the Atmega with the 32-input firmware. Since I was upgrading from an old version, I cleared out the EEPROM at startup, and I ended up with the VU.
OK, great! Everything was working well, so I went to play around in the menus. No more than a few seconds would pass before I would get pushed into one of the channel configuration screens, regardless of where I was in the menu at the time (channels 31, 27 and 29 popped up the most).
Less frequently -- and this seemed to happen most regularly when I was pushing or holding a combination of buttons (i.e. to get to the very beginning and end of the menu) -- the MIDI activity light would turn on and the menu would go crazy by quickly moving in random directions through the channel configurations, much like the keys had gotten stuck. Power cycling the board is the only way I found to get out of this condition.
I double-checked the keyboard, and it appears to be constructed properly. Each button also works just fine until the keys "stick".
Has anybody else seen this behavior?