key `+space without function; ö,ä and ü in some programs

after installing `language-pack-de` and `language-pack-gnome-de` and setting keyboard layout to `German` the key <kdb>`</kbd>+<kbd>Space</kbd> is dead (I have to insert ` by pasting). The keys `ö`, `ä` and `ü` work in some programs (e.g. `firefox`), but not in others (e.g. `gedit`). I installed all recommended packages for language support for german as suggested by `Language Support`. `German` is the only language and locale set up and the only keyboard layout.

ProblemType: Bug
DistroRelease: Ubuntu 14.10
Package: ibus 1.5.8-2ubuntu2
ProcVersionSignature: Ubuntu 3.16.0-23.31-generic 3.16.4
Uname: Linux 3.16.0-23-generic x86_64
NonfreeKernelModules: zfs zunicode zavl zcommon znvpair
ApportVersion: 2.14.7-0ubuntu8
Architecture: amd64
CurrentDesktop: Unity
Date: Mon Oct 27 21:50:56 2014
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 SHELL=/bin/bash
SourcePackage: ibus
UpgradeStatus: No upgrade log present (probably fresh install)