Tracking state changes using yield

I have a function which I use to change the enum state of my character. When the state changes I set stateJustChanged to true, then use yield to wait one frame before turning stateJustChanged to off. Which normally works fine. Unless on that second frame I again change state, in which case stateJustChanged remains off, not registering that the state has just changed.

Also, sometimes the state change isn't registered right away...

Is there a better way of doing this?

public var          state:CharacterState = CharacterState.Off;
public var          stateJustChanged:boolean;
function ChangeState(newState:CharacterState)
    {
    state = newState;
    stateJustChanged = true;
    yield;
    stateJustChanged = false;
    }