Ok, I know this look like a monologue but anyway I solved the problem by myself.
So if this happens to anyone, you have to find all the kmix file (alt f2, kfind, then search *kmix*) and delete them. Images doesn't matter (png files) but delete kmix folder and other kmix files (some of them need rood privileges, that you can reach by the context menu root action). I suppose I didn't do it well first time because kmix files are not situated in exactly same place in all distributions. You should do these operations with kmix desinstalled first (or maybe killed its enough). Then you reinstall it, reboot, and it's ok. Apparently this is due to a corrupt profile... I hope no grand ma will ever get this bug, because high cpu make computer unusable.