When this happened with my old Touch Pro, it was a sign that the keyboard connector was coming loose and eventualy failing entirely. It was a common problem with the Touch Pro, but keyboard problems seem rare with the Moment.
Just to be sure, do a hard reset- menu > Settings > Privacy > factory data reset
If a flash or hard reset didn't correct it, I would take it in to a repair center. You should still be under warranty. Good Luck.