[SalesForce] Standard Save button on visualforce page doesn’t update standardController

I'm trying to save a checkbox value (and eventually a pulldown list of invitee status) with a standard Save button but all it does is refresh the page. I want to update the custom object Event_Attendance__c with the status and Attended checkbox. Here is the code:

<apex:page standardController="Event_Attendance__c" extensions="InviteeListController">
    <apex:sectionHeader title="Event Attendance" subtitle="{!eventDate} - {!eventName}"/>
    <apex:pageBlock title="Invitees" mode="edit">
    <apex:form >
    <apex:actionFunction name="getInvitees" action="{!InsertInvitees}"  rerender="allPanel" />
   <apex:outputPanel id="allPanel">
      <apex:outputPanel rendered="{!NOT(myFlag)}">
     <script>
           window.onload=function()
           {
             getInvitees();
           };
        </script>
      </apex:outputPanel>
     <apex:outputPanel rendered="{!NOT(myFlag)}">
       <apex:pageBlockTable value="{!eventinvitees}" var="eventinvitee">
            <apex:column value="{!eventinvitee.Relation_id__c}"/>
            <apex:column headerValue="Invitation Status" value="{!eventinvitee.Status__c}"/>
            <apex:column headervalue="Attended">
            <apex:inputCheckbox value="{!eventinvitee.Attended__c}"/>
            </apex:column>
        </apex:pageBlockTable>
        <apex:commandButton action="{!Save}" value="Save"/>
            </apex:outputPanel>
    </apex:outputPanel>
</apex:form>
    </apex:pageBlock>
</apex:page>

Here is the controller code:
public with sharing class InviteeListController {

      string eventid=ApexPages.currentPage().getParameters().get('event_id');
      public string eventName {
        get {eventName = ApexPages.currentPage().getParameters().get('event_name');
        return eventName; }
        private set;
        }
      public string eventDate {
        get {eventDate = ApexPages.currentPage().getParameters().get('event_date');
        return eventDate; }
        private set;
        }
      public Boolean myFlag{get; set;}

public InviteeListController(ApexPages.StandardController controller) {
       myFlag=false;

      }


public void InsertInvitees()
{

if (!myFlag)
{
Integer inviteecount = [SELECT COUNT() FROM Event_Attendance__c WHERE EventID__c = :eventid];
if (inviteecount== 0){

     getinvitees= [SELECT RELATIONID, EVENTID, STATUS,  RESPONDEDDATE, RESPONSE FROM EventRelation WHERE EVENTID = :eventid];
      List<Event_Attendance__c> insertinvitees = new List<Event_Attendance__c> ();
      for (EventRelation a : getinvitees){
        Event_Attendance__c ea = new Event_Attendance__c();
        ea.EventID__c = a.EVENTID;
        ea.Relation_id__c = a.RELATIONID;
        ea.Status__c = a.Status;
        ea.Event__c = eventName;
        insertinvitees.add(ea);
      }

        insert insertinvitees;
        myFlag = True;
      }
    }
    eventinvitees= [Select Status__c, Attended__c, Relation_id__c, EventID__c, Event__c FROM Event_Attendance__c WHERE EventID__c = :eventid ];
}

public List<Event_Attendance__c>eventinvitees{get; set;}
public List<EventRelation>getinvitees{get; set;}    

}