For some time now, it has not been possible to copy GUI components in the NetBeans GUI editor. Apparently, the KDE clipboard doesn't play well with NetBeans GUI copying. Until Plasma 5 arrived, the clipboard tray icon was provided by klipper and you could get GUI copying to work by just selecting Quit from the tray icon popup menu. Klipper was even nice enough to ask if you want it to start again automatically at next login. Of course, you didn't need to log out and log in again, you just called up krunner with Alt+F2 and typed klipper.