An anonymous reader writes "Select to copy and middle-click to paste. That's very convenient usability feature associated with UNIX graphical environments. But it is confusing for new users, so the ability to middle-click paste was briefly removed from GNOME 3.10. It was restored few days later, but with clear message: middle-click paste will be permanently removed from next GNOME version."
I hope that "we'll defer this change until the next cycle" also means that it's getting re-thought, rather than just delayed.