As was discussed by the team the other day, copying keyframes (to copy/paste buffer) in DopeSheet/Graph Editor no longer relies on the selection status of the F-Curves, but rather on the selected keyframes only. This should be less confusing... However, pasting keyframes still relies on having F-Curves selected to aid in the channel-matching process. There is still a lot of room for improvement in this area though (as noted in the code!).