Sporadic keyboard jamming on lightdm; problems with sessions after

[Adam Funk]

A relative has a new laptop with a fresh install of 14.04 on it.
Occasionally the lightdm login screen doesn't accept keyboard input,
so he can't log in, although the pointer still follows the mouse.  We
think it's more likely to happen when he points the mouse at the
battery icon, but it can happen without doing that.  We tried using
Ctrl-Alt-F1 to log in through a virtual terminal & do 

sudo /etc/init.d/lightdm stop
sudo /etc/init.d/lightdm start &

with the "&" because otherwise the start hangs on to the terminal
instead of detaching, as I'd expect.  Then we hit Ctrl-D & Ctrl-Alt-F7
to get back to the GUI login.  Logging in seems to work, but trying to
do anything with the network manager applet throws up an error dialog
like "no session for user 1001" (where 1001, for example, is actually
the user logged in through the GUI).

Any suggestions for fixing or debugging?

Thanks,
Adam