To notify someone, say me RememberSchiff, of the post you are typing. You don't just quickly type @RememberSchiff in the post.
Slowly type @ then R and watch a non-scrollable dropdown box appear with some entries
As you type more "correct" letters, the dropdown box gets closer to the desired name.
Move mouse cursor to RememberSchiff in dropdown and click. The dropdown box disappears , leaving the notification which is activated when you Save post.
@RememberSchiff