Q: I keep calling expandItem(itemId) and clickItem(itemId) but they do not have any effect. They only expand or select the target menu item, but they don't execute the actions of the menu item, like calling the function specified in the xml file or triggering the appropriate event. How can this be fixed ?

A: Indeed, the clickItem() and expandItem() methods do only what their name implies and nothing else. If you also would like to receive an event and have the function from the xml file called by the component, then you need a few extra lines of code, besides the one of the two function calls:
   
    accTreeMenu.clickItem(itemId); // or accTreeMenu.expandItem(itemId);
    // the next line of code will execute all the actions associated with the navigation mode: press, release or rollover
    accTreeMenu.getItemById(itemId).itemAction(accTreeMenu.navigationMode);
    var eventType:String;
    switch(accTreeMenu.navigationMode) {
        case "press" : eventType = "onPress"; break;
        case "release" : eventType = "onRelease"; break;
        case "rollover" : eventType = "onRollOver"; break;
    }
    accTreeMenu.dispatchEvent({type:eventType, target:accTreeMenu, item:accTreeMenu.getItemById(itemId)});