ubuntu 14.04 apt/aptitude autocompletion with oh-my-zsh not working

I've recently begun to use zsh with oh-my-zsh in a Ubuntu 14.04 server. The problem is that autocompletions of the debian plugin do not work, i.e. ``` ai something<TAB> ``` does not autocomplete. Of course ``` aptitude install somethi<TAB> apt-get install somethi<TAB> ``` do work correctly. The git plugin of oh-my-zsh also works without any problems whatsoever. So I've begun to wonder if anyone has a solution to this problem. Here are some related packages if someone needs more info: ``` ⇒ aps zsh completion p bash-completion - programmable completion for the bash shell v bash-completion:i386 - p fatrat-czshare - fatrat plugin allowing download and upload to czshare p fatrat-czshare:i386 - fatrat plugin allowing download and upload to czshare p fizsh - Friendly Interactive ZSHell v git-completion - v git-completion:i386 - v ncmpcpp-completion - v ncmpcpp-completion:i386 - i zsh - shell with lots of features p zsh:i386 - shell with lots of features p zsh-beta - transitional package to zsh p zsh-beta-doc - transitional package to zsh-doc i A zsh-common - architecture independent files for Zsh p zsh-dbg - shell with lots of features (debugging symbols) p zsh-dbg:i386 - shell with lots of features (debugging symbols) p zsh-dev - shell with lots of features (development files) p zsh-dev:i386 - shell with lots of features (development files) i zsh-doc - zsh documentation - info/HTML format p zsh-lovers - tips, tricks and examples for the zsh p zsh-static - shell with lots of features (static link) p zsh-static:i386 - shell with lots of features (static link) p zshdb - debugger for Z-Shell scripts ```