Comment 12 for bug 426641

The command 'apt-cache show checkbox-gtk | grep Version' isn't a good way to check what version of a package you have installed as this only shows the version available on the archive. A better way to check what version of a package you have installed is either 'apt-cache policy checkbox-gtk' or 'dpkg-query -l checkbox-gtk'.

Regardless, the manual for checkbox, checkbox-cli and checkbox-gtk are provided by the file '/usr/share/man/man1/checkbox1.gz' which is included in the package checkbox. I'm not quite sure why man checkbox would work and the others would fail.