This was a tricky one: when I tried inputting some japanese text with skim, it wouldn't work in KWord. Turns out that when KWord gets a IMComposite event, it (indirectly) calls this function. That would then unconditionally update that KAction, that then would update a QCombobox to set the current text, and that then would reset the inputcontext on the poor old canvas, thus resulting in a loss of your poor hiragana each time skim would compose one.
I fix this by checking if the fontsize and font family actually changed. Since I assume it won't change in the middle of an IMStart-IMEnd sequence, this fixes the input with me.

From what I understand, this would basically mean that Japanese input would be impossible without this patch. However, I think I recall actually being able to do that in KWord, so I'm inclined to think that it's partially caused by qt-immodule. Anyway, the CCBUG seems related, but I'm going to check this with someone who actually has a real Japanese keyboard (Kiruwa) and maybe close it if he can confirm this a bit better.
CCBUG: 41380