BUMP...
Had an issue with my Harmony 880 today.
Some of the buttons were all messed up: "Activities" sent the "7" key, "Off" didn't work, etc. Reprogramming didn't solve the issue. The battery read fully charged.
After some Googling I tried a cold restart as suggested by others. It fixed the problem. Though reprogramming says it is "rebooting" the remote, it isn't a cold boot. To get that you have to:
1. Take out the lithium battery.
2. Plug the remote into a USB port on the computer for a few moments, get it through it's test phase and to the point it tells you the battery needs charging (ah, funny).
3. Unplug from the USB, put back in the battery, let it restart, test, etc.
It fixed my problem. It's been almost two years glitch-free with the 880. I assumed my battery was starting to go. I'll watch it closely. Can't live without the all-in-one remote.
TJR