Its hard to describe this, but I have taking some screen shots and I will try anyway.

When in your survival player inventory, and you mouse over your 2x2 crafting box (input or output), the icons in the armor slots showing what type of armor goes there will vanish.

This also happens when you have an item or block in the 2x2 crafting box (input) but if their is an item or block in the output slot, the armor icons do not vanish.

Something else that causes the armor slot icons to vanish is mousing over them. If you mouse over the boots slot, nothing happens, but if you mouse over the pants slot, the boots icon will vanish. If you mouse over the chest plat slot or the helmet slot, all armor icons beneath them will vanish.