When one opens any inventory and clicks on a sandwich to move it, the numbers displayed on other item stacks will render over the sandwich item model, as opposed to under the sandwich, the way all other items draw over stack numbers. This was tested with the chest inventory, the survival and creative mode inventories, the furnace inventory, and the brewing stand inventory, as you can see below.

The issue is that the sandwich icon is in fact a 3D model. Since it's not that tall, the numbers seem to be rendering over it...