I can confirm that this happened to me also (yesterday). My fix was to reboot! I'm researching this, and will post any progress in this thread.

Edit: I cannot reproduce this problem today! Is this a consistent problem, or did it just happen once? Did you try disconnecting the attached USB device (keyboard) by tapping the USB icon in the status bar before unplugging the keyboard? That is the *safe* way to disconnect USB devices... Interesting that I cannot reproduce it again.