Jeff: Sorry, I just now got around to replying to your help above. Here's what the results were:
-First letting you know the specific keyboard shortcut I prefer and all this pertains to is the "shift/command/4". Second I tried copying different areas on screen like email, website, desktop, etc.
1)Restarted in Safe Mode, did not copy first try, did 2nd.
2)Restarted computer regularly, did not copy first try, did 2nd
3)Noted the Preview in lower dock was sometimes on and sometimes off, didn't seem to matter-even if ON sometimes it copied on first try sometimes not (intermittent it seems now)
4)Setup 2nd user and logged in-when tried to copy I saw a window on lower right appear then slide off to right and found it on desktop. (This never happened in Safe nor non-safe mode)
5)Deleted 2nd user and restarted regularly, did not copy first try, did 2nd
6)Restarted computer-worked first time. (seems to happen off and on, but "frequently")