In KDE's control center, there is an option to clear all the MRU (most recently used) stuff - most recent apps, thumbnails, cookies, etc. - found in Control Center -> Security & Privacy -> Privacy. One of the things this is supposed to let you clear is your web history. The problem is that, even if web history is selected for clearing, it will usually not be cleared upon clicking the "Clean Up" button. If you click "Defaults", then "Select All", before cleaning up your MRUs, it sometimes works... And sometimes not.

This is not a major issue, since web history is not accessible remotely, and you can still clear it from within Konqueror, but it is rather annoying.