I also have this bug.
Same laptop (Lenovo thinkpad X1 carbon gen2). Ubuntu 14.04, fresh install (today).
This blog post talk about the same bug : http://www.adventuresinoss.com/?p=3698 . It identifies the origin as "xhci_hcd".
One solution is to deactivate the USB3 in the BIOS.
I also have this bug.
Same laptop (Lenovo thinkpad X1 carbon gen2).
Ubuntu 14.04, fresh install (today).
This blog post talk about the same bug : http:// www.adventuresi noss.com/ ?p=3698 .
It identifies the origin as "xhci_hcd".
One solution is to deactivate the USB3 in the BIOS.