I'm having the same problem but here is how it goes for me. I use a blue tooth KB most of the time. About 3 to 5 times a day, the bluetooth KB stops working but only the letters and numbers. The arrows and other commands still work. If, while that's happening, I try to use the KB on the actual Macbook, it appears to have the same problem, letters don't work, but arrows and other commands do. Then, after about 45 seconds to a minute. everything goes back to normal. is anyone else having this problem?