# docker version
Client version: 0.6.4
Go version (client): go1.1.2
Git commit (client): 2f74b1c
Server version: 0.6.4
Git commit (server): 2f74b1c
Go version (server): go1.1.2
Last stable version: 0.6.5, please update docker
# apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages have been kept back:
lxc-docker
0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded.
The same problem just occurred again upgrading from Docker lxc-docker-1.4.1 to 1.5.0 (on Ubuntu 14.0.4 for me).
Forcing
sudo apt-get install lxc-docker
fixed the problem: