This is reproducable 100% of the time.
Using the printscreen button in the game client will take a screenshot and show the little notification as intended, but after that my clipboard becomes hard-locked until I exit the game client. This is on Win10.
While my clipboard is “locked” I can copy and cut, but can not paste no matter what I do. Again, it’s resolved when I exit the game client.
Late edit: This is a default hotkey on Windows to copy an image to the clipboard - Printscreen = copy all monitors as a single, wide image, ALT+Printscreen = copy current window