Comment 11 for bug 1521689

Well, in case someone else needs it in the future. The issue is because the icons on the theme are not yet created. So depending on which theme you're using some icons will not exist. In the case of Ubuntu 16.04 some icons (specially the skip transaction) don't exist. A temporary fix:

Execute `kcmshell4 icons` in a console and select `Oxygen`. This theme seems to have all of them.

source: http://askubuntu.com/questions/637051/ubuntu-15-04-change-kde-applications-icons