I'm currently running Plasma 5.2.2 on Kubuntu 15.04. What I've done is pressed the button to clear the history of the clipboard stored in the default clipboard manager applet. It gave me a prompt to confirm clearing the history, with options "yes" or "no." There was also a checkbox offering to prevent the message from displaying in future. I initially pressed that checkbox, but then had a moment of doubt as to whether I wanted to clear the history at this time, so I pressed "no." Now, pressing the "clear" button in the clipboard manager applet doesn't do anything. This seems illogical. A better solution, as far as I can see, would be to always prompt the user when pressing the button until they've pressed the checkbox + "yes." Perhaps the "no" option should act more like a "cancel," not saving the checkbox's setting. What's worse is that there is no graphical option within the applet's settings to reset the confirmation prompt. I am not sure if I should file a bug report on this issue, going forward.

Also, I did find a fix for the problem, which I'll include if anyone else is experiencing this issue:

Inside the file "~/.config/plasmashellrc" there is this option: "really_clear_history=false". Change "false" to "true," so it reads: "really_clear_history=true". After restarting Plasma (log out and back in), the clipboard applet now clears when the button is pressed.

Edit: I maybe should have put this post under "Plasma 5" instead of "Plasma." If this is the case, I apologize, and would appreciate a mod moving the thread.

THANK YOU!!!