:help word[CTRL-D] doesn't search help

I launch vim by typing it's name. Inside vim I type :help word[CTRL-D]

EXPECTED RESULT: search the vim documentation

ACTUAL RESULT: I get the : command history

The CTRL-D sequence is described in the :help help file. This is a very important feature for me and I suspect other vim users. This problem does not exist on 10.04.

WORKAROUND: tab key instead of CTRL-D, but this isn't mentioned in the documentation.

I can start vim either in a gnome-terminal with or without byobu running screen, I can also start via a virtual terminal by pressing ctrl-alt-F2 and I get the same result. All three entries of vim :set term?. vim :echo $TERM and vim :!echo $TERM are consistent in both cases, as screen in the first case and linux in the second case. With all three in agreement there is only the vim configuration left for interpreting the following command, right?

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: vim 2:7.3.429-2ubuntu2.1
ProcVersionSignature: Ubuntu 3.2.0-41.66-generic 3.2.42
Uname: Linux 3.2.0-41-generic x86_64
NonfreeKernelModules: fglrx
ApportVersion: 2.0.1-0ubuntu17.2
Architecture: amd64
Date: Mon May 13 16:10:08 2013
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Alpha amd64 (20120315)
MarkForUpload: True
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: vim
UpgradeStatus: No upgrade log present (probably fresh install)