Debian ships natively with vim-tiny but one might need the full vim, e.g. for syntax highlighting which is pretty handy. In various situations vim and vim-tiny do not work side by side, causing the funny “E319: Sorry, the command is not available in this version” having syntax on in your /etc/vim/vimrc.
While this is pretty annoying, the solution is rather simple – wipe vim and vim-tiny, reinstall vim and re-set the default editor.
# apt-get remove --purge vim vim-tiny # apt-get install vim # update-alternatives --config editor