Or, in other words, your keyboard will no longer work.
The cause, which I only found out by chance, AFTER I changed the batteries in my wireless keyboard. When I say close, I mean arm length. The HTC Desire power charger throws out enough electrical interference, to cause the keyboard to drop characters.
Now I know the answer, I can search Google and find this helpful Microsoft article:
Troubleshoot response failures in wireless keyboard or mouse


