Hi Spencer:
Roberts Rules, Section 3 (General), Betting & Raising, rule 11 addresses this pretty well for cash games:
"11: Deliberately acting out of turn will not be tolerated. A player who checks out of turn may not bet or raise on the next turn to act. A player who has called out of turn may not change his wager to a raise on the next turn to act. An action or verbal declaration out of turn is binding unless the action to that player is subsequently changed by a bet or raise. If there is an intervening call, an action may be ruled binding."
In your example, Seat 4 made a verbal declaration out of turn to raise the action. At the time of 4's declare it was only 2 units to him.
Now, per Rule 11 above, if the action is sugsequently changed by a bet or raise, his declare is not binding. That's exactly what happened: the action was backed up to the rightful bettor (Seat 3) and 3 changed the action to Seat 4. 3 changed it from 2 units to 10 units. So, based on this I would rule that Seat 4 is not bound by his declaration of 11 units and can take any action he wants: call, fold, or raise. BTW, this is similar to TDA Rule 29 for tournament play.