Clipboard Manager: New shortcut defined by me not working

I create a new button in Clipboard Manager to convert letters to uppercase and give it a new shortcut "Cmd+U".
Then I open Clipboard Manager, select a text and press "Cmd+U". The system just issued a beep and nothing happened. No text pasted.


For me the shortcuts do work, but incorrect shortcuts are displayed as tooltips when you hover over a button. Eg. i change the shortcut to Cmd+A in the transformer settings as above, but Ctrl-V is displayed in a tooltip.

The shortcut still doesn't work me.
BTW I also noticed the shortcut is changed to a different one.