When I copy something from a file opened in mousepad, then close mousepad and try to paste it in another mousepad window or another application, it doesn't work. mousepad seems to clear the clipboard, both Ctrl-V as the builtin Linux method, when closing. It only works when I keep the mousepad window open. Reproduce: 1. Copy something from a mousepad window 2. Close that window 3. Try to paste it somewhere else. Actual result: The copied text isn't pasted. Expected result: The text is pasted and it will be in the clipboard memory until it's overwritten.
This is just the way X works.You can't copy from ANY closed application. Try copying from Firefox window, closing all of Firefox, and then pasting into Mousepad - nada.