The bug

The icons.png file contains an unused background slot texture for hunger icons which is white, which appears to be an analogue of the respective heart background texture, which appears when either taking damage or healing. However, this texture seems to be unused from hunger, and does not appear either when the bar empties or after eating.

How to reproduce

1. Cause the player to take damage
   1. Notice how the health bar's whole background flashes white
2. Heal said damage through any desired means
   1. Notice how the background again flashes white
3. Cause the player's hunger bar to empty
   1. Notice no flashing
4. Now refill the bar through eating
   1. Again, notice no flashing

Other thoughts

As stated before, splitting icons.png into multiple sprites is something I'd recommend and would probably help stop unused icons from accumulating in future.