I was just looking around at other packages to see what Group: tag should go on a -doc subpackage. It looks like Documentation is the right group, but I noticed that this is rather inconsistent in the official packages.
exim-doc Documentation gtk-doc Development/Tools kernel-doc Documentation nasm-doc Development/Languages selinux-doc System Environment/Base sendmail-doc Documentation tclx-doc Development/Languages tetex-doc Applications/Publishing tix-doc Development/Languages xorg-x11-doc Documentation
Given that the Group: tag is essentially meaningless, I wasn't sure this justified mention in bugzilla, but it probably should be fixed.
Steve