Why does this part of code run twice?

Questions & Answers
1

I am making a basic inventory with stacking and for some reason whenever i click on the item it subtracts 2 instead of just 1. Can anyone help me? Thank you

void OnGUI () 
	{
		GUI.DrawTexture(windowRect, inventoryBackgroundTexture);

		for (int x=0; x<across; x++)
		{
			for (int y=0; y<down; y++)
			{
				Rect buttonRect = new Rect(_offset*2+buttonSize*x, _offset*2.5f+buttonSize*y, buttonSize, buttonSize);

				if (inventory[x, y] != null)
				{
					if (inventory[x, y].itemCount > 0)
					{
						GUI.DrawTexture(buttonRect, inventory[x, y].texture);

						Vector2 mousePos = Input.mousePosition;
						mousePos.y = Screen.height-Input.mousePosition.y;

						if (buttonRect.Contains(mousePos))
						{
							if (Input.GetButtonDown("Fire1"))
							{
								SubtractItem(x, y); *** This part runs 2 times ***
							}

							GUI.DrawTexture(buttonRect, hoverTexture);
						}

						if (inventory[x, y] != null)
						{
							GUI.Label(buttonRect, inventory[x, y].itemCount.ToString(), itemCountStyle);
						}
					}
				}else{
					GUI.DrawTexture(buttonRect, blankTexture);
				}
			}
		}
	}
2

Probably you have two cameras with Gui Layer on them? You should move any input handling out into the Update() function.