Why does adding a GameObject to another change the scale, when something that already exists as it's child's scale is fine?

I am building a map of my world.

 created_tile = GameObject.Instantiate (mapPiece, tile_location, Quaternion.identity) as GameObject;
 
 
                     //created_tile.transform.Rotate (0, 0, 0);
 
 
                     if (created_tile) {
                         created_tile.transform.parent = mapPanel.transform;
                         created_tile.layer = LayerMask.NameToLayer ("UI");
                         drawnMap [x, y] = created_tile;
 
                     }

mapPanel's localScale is 1,1,1

my created_tile's localScale is 1,1,1

however when I add created_tile.transform.parent = mapPanel.transform the created_tile's local scale becomes 0.8,0.8,0.8

if I do created_tile.transform.SetParent(mapPanel.transform, false) then the tiles are not positioned in the right place anymore.

What can I do?