The applet menu is stuck, containing two disabled entries, 'Clipboard is empty' and 'Clear'. It cannot be closed. The applet button looks depressed and irresponsible.
(Sad. What did you do to make it look depressed exactly? J/K) This sounds like an older version. Can you right click on the plugin, go to About and tell me which version you have? Or you can use your distributions package manager.
It's 1.1.3.
It would be good if you can switch to version 1.2.1 to reproduce. There won't be fixes for 1.1.x, however, the code responsible for the menu didn't change between this two versions so it shouldn't matter. Also can you describe a step-by-step so I can try to reproduce it. Did you click, or run the popup command?
Any news here? Also have you been using the xfce4-popup-clipman command?