Setting localposition to a vector 3 sets everything but the x

I have code that I use to attach a little cursor icon to a UI Button that is part of a menu. When the button is selected, the script attaches the cursor to the object and sets the rect transform of the cursor so it appears just to the left of the menu button.

Here's the code: (the width of the cursor is about 25)

 public void OnSelect (BaseEventData eventData)
     {
         GameObject cursor = MC.CursorInstance();
         RectTransform thisRect = cursor.transform as RectTransform;
         cursor.transform.SetParent(this.transform);
         thisRect.anchorMin = new Vector2(0, 0.5f);
         thisRect.anchorMax = new Vector2(0, 0.5f);
         thisRect.pivot = new Vector2(0f, 0.5f);
         thisRect.localScale = new Vector3(1, 1, 1);
         thisRect.localPosition = new Vector3(-thisRect.sizeDelta.x, 0, 0);
     }

Not sure why, when selecting the button, the cursor position is set to 13 instead of -25 like I was expecting. Any reason why this might be happening?