I wonder if it's a bug or not (or distro-related error). Let me describe it. Nepomuk or more accurately Strigi runs at startup and consumes much cpu time. Usually stop indexing doesn't work and I have to kill it in system activity. But there's a problem there. Take a look at first screen:
It's look like the system activity is suspended. On the other hand top output shows accurate outcome. So I have to use top to kill nepomuk (or rather virtuoso).
Once again the cpu plasmoid also shows accurate(?) outcome:
Having killed virtuoso system activity backs to normal state: