Example: Cut something to the clipboard in Firefox.
Close Firefox.
Try to paste into a GNOME application.
Ta-DA! Look ma! No data!
That's the bug.
Lather, rinse and repeat for GNOME/KDE pasting, too. Although there are moves afoot to develop a common clipboard, the movers and shakers (of which the aforementioned Mr Nickell is one) are apparently easily distracted by shiny things.