Dealt with this type of thing at work, when it's looking for a string to match it can't do it immediately because it's waiting to see if the next thing you type is something that would break the match or match something else. If you have Ant = Dec once you've typed "Ant" it's waiting to see if you press space, meaning it has a full string it confirms as a match and changes it to Dec, or if you go on to type Antidisestablishmentarianism, which is not a match. And you don't want to end up with Decidisestablishmentarianism, do you.