In Terminal land, Ctrl+C has meant Cancel longer than it's meant copy. Shift + Insert does what you think Ctrl+V will do.

Also, there's a separate thing that exists in most window managers called the Primary buffer, which is a separate thing from the clipboard. Try this: Highlight some text in one window, then open a text editor and middle click in it. Ta da! Reminder: This has absolutely nothing to do with the clipboard, if you have Ctrl+X or Ctrl+C'd something, this won't overwrite that.