why does my code tag objects it's not supposed to?

I'm trying to randomly generate a dungeon based on predefined rooms. Every time a new room is created, it is supposed to remove the "Endpoint" tag, so that room will not be included in the next search for a liable room. Each of these rooms has a child, endPoint, from which the next room will be built on. each endPoint is tagged "Endpoint" like in the code. The code -does- "Untag" the objects like it's supposed to, but for some reason or another it will ocassionally "Untag" the newly created room, resulting in a random dungeon sometimes from 4 - 6 rooms long.

     function Update () {
 
 timer++;
 
 if (timer >= 60)
     {
         timer = 0;
         MakeDungeon();
     }
 }
 
 
 
 function MakeDungeon()
 
 {
 
 endPoints = GameObject.FindGameObjectsWithTag("Endpoint");
                                                         // picks a random rooms endpoint.
 var randomPoint:GameObject = endPoints[Random.Range(0,endPoints.length)];
 
 //var room: Transform = randomPoint.transform.parent;
 
 Instantiate(verticalHall,randomPoint.transform.position,Quaternion.identity);
             randomPoint.gameObject.tag = "Untagged";
         
 }