Comment 1 for bug 35875

This is covered by http://www.jwz.org/doc/x-cut-and-paste.html and occurs because the app that you did the copy in has to send the selection to other apps (so if it is no longer running this is not possible). The only way round this is with a clipboard daemon (and that raises questions about what to keep when content negoiation is possible).

This is probably a wishlist item.