Many KDE apps (Dolphin, Kate, Okular, etc.) let you configure their tool bars (or get rid of them entirely) and set them to show just icons, text, or both (with the text to the side or below). It's the kind of thing most people won't bother with, but for frequently used applications it's nice to be able to customize it to suit your needs. It's done via a config option though, not by dragging menu items to the toolbar (which strikes me as something you could initiate by mistake).