Comment 302 for bug 11334

(In reply to comment #9)
> This is a consequence of the X11 clipboard design and not LibreOffice
> specific. As such, there's not much LibreOffice itself can do about this on
> its own.

I'm not sure that "there's not much LibreOffice itself can do"... have you seen that specifications, for ways to store clipboard content after program exit?
https://wiki.ubuntu.com/ClipboardPersistence
http://freedesktop.org/wiki/ClipboardManager/