I've installed iBus and ibus-mozc, an input method engine of Japanese from the repository on Kubuntu 12.04.
Then attempted to enable mozc from
Preference > "Input Method" tab > "Select Input Method" combo box.
However, there is no choice to select, so I couldn't enable mozc.
I also tried ibus-anthy, another legacy Japanese input method, but the situation was the same and I couldn't use anthy.
Same problem is also occuring in openSUSE 12.1, so I don't think this is distribution-specific problem.
In addition, this trouble also happened when I installed ibus-pynin, so this is not Japanese-specific problem.
Any idea to find the cause of this trouble?