Thank you for taking the time to report this bug and helping to make Ubuntu better. Please answer these questions:
* Is this reproducible?
* If so, what specific steps should we take to recreate this bug?
This will help us to find and resolve the problem.
By the way, the auto-completion for the apt-get command works fine for me. If it's on a fresh install, perhap's this completion needed an "apt-get update" before.