Salesforce ID issue - with Tests! Both the Picklist and the String values here fail

Salesforce IDs are broken in Summer 13

@isTest
private class TestIDs {
  
@isTest static void test_method_one() {
    Map<Id,SObject> oldMap = new Map<Id,SObject>();
    
    Opportunity o = new Opportunity();
    o.Name = 'Test Oppty';
    o.StageName = 'Prospecting';
    o.CloseDate = System.Today().addDays(5);
    Database.Insert(o);
    oldMap.put(o.Id, o);
    
    TriggerHandler th = new TriggerHandler();
    SObject sobj = oldMap.values()[0];
    
    Boolean isPicklistId = th.isInstanceOf( sobj.get('StageName') );
    Boolean isDateId = th.isInstanceOf( sobj.get('CloseDate') );
    Boolean isStringId = th.isInstanceOf( sobj.get('Name') );
    
    System.AssertEquals(isPicklistId, false); //==> THIS FAILS
    System.AssertEquals(isDateId, false);
    System.AssertEquals(isStringId, false); //==> THIS FAILS
  }
}


public class TriggerHandler{
  public TriggerHandler(){}
  public Boolean isInstanceOf(Object obj){
    if(obj InstanceOf Id){
      return true;
    }else{
      return false;
    }
  }
}

Hello readers of this Gist;

This is a way to reproduce the errors in Summer '13 related to Ids. What is happening:

When you use SObjects, you are given Objects back when you do a .get(). When you pass an object to instanceOf method comparing to type Id. The tests on line 21 & 23 fail.

If you are at Salesforce.com & would like to discuss these, please contact me.