Comment 3 for bug 255058

Changing the binding of autocompletion function to command from this:
  complete -F _chown $filenames chown
to this:
  complete -F _chown -o nospace chown
avoids both the quotting of the colon and the adding of a trailing space added (both actions are performed by Bash's autocompletion features, so the package selection is probably right).

The relevant line is in /etc/bash_completion.

The problem of this solution is that it breaks the proper filename completion for 'chown'.