Comment # 2 on bug 1146018 from Marc Chamberlin

Not just applicable to Tumbleweed, Leap 15.3 and 15.4 also have the issue of
Cut/Copy and Paste not always working. Cut and Copy does seem to always put
what is selected at the top of the clipboard stack, but Paste does not always
recognize that there is something to paste from the clipboard stack. Definitely
a problem across many KDE applications.