Sometime in Minecraft development after 1.2.5, several textures were broken, and because the are small features, they went un-noticed. This is most likely related to Wither-related additions (similar to how paintings broke, and shortly after a wither painting is added).
The textures that affected are:
Transition icons (in /gui/icons.png). Health/hunger icons that should display when health/hunger is gained or lost no longer display after 1.2.5. I noticed that this was broken only because Wither hearts were added to the GUI, and I went to test them, and I wanted to see how the transition icon looked, but it never appeared
texture pack no pack.png icon (/gui/unknown_pack.png). This file does not load anymore. Instead, the game uses the default pack.png.
Note that these changes occur in vanilla and any texture pack, but work how they used to if the .JAR is replaced with a .JAR from 1.2.5.
What I expected to happen was:
Features that worked in previous versions of Minecraft that were not noted of changes in change logs not to be changed.
What actually happened was:
Small features were broken after 1.2.5, but because they were small, nobody noticed.
Steps to Reproduce:
1. Download example_pack.zip (attached)
2. Download example_pack_no_icon.zip (attached)
(in 1.4.5 or 12w50a)
3. Start Minecraft, navigate to the texture packs menu, change the selected texture pack to example_pack.zip
4. Take note of what the icon for the pack is for example_pack_no_icon.zip while you have eample_pack.zip as the selected pack
5. Start a new survival world
6. Find a way to cause a large amount of damage to the player, and watch the health bar. Fall damage is the best for this.
7. Repeat steps 1-6 in a 1.2.5 version of Minecraft.
Also attached is a picture of the transition icons that should display but no longer do (they are in the red rectangles).