From Minecraft Wiki
1.8.4 is an update to Minecraft which was released on April 17, 2015 to fix various exploits and important security vulnerabilities, as well as some other minor issues. 1.8.4 is compatible with 1.8 – 1.8.3 servers.
- Player head skins can no longer be loaded from arbitrary servers.
- They must now be loaded from the official Mojang servers.
- Player head skin files are now required to be a .png file.
- Traveling through a nether portal no longer places the player outside the portal.
- Pets no longer follow the player in spectator mode (wolf and ocelot).
- 15 issues fixed
- From released versions before 1.8.1
- MC-10979 – Hardcore single player has repeating screens and weird links
- MC-46771 – Pets follow spectator
- MC-49060 – Chest sticking open when teleported while GUI is up
- MC-61758 – Vines no longer spread correctly in corners
- MC-61895 – Crash when putting the default spawn egg in Monster Spawner
- MC-68642 – Certain characters cannot be typed on certain keyboard layouts ("AltGr" behaving like "Ctrl")
- MC-73504 – Nether portals place players two blocks beside the portal
- MC-77371 – Mac OS X weird Keyboard when Native Fullscreen
- MC-78020 – "User (formerly known as olduser) has joined" shows multiple times
- MC-78491 – Custom player heads exposing player's IP address
- MC-79152 – Security vulnerabilities involving skulls
- MC-79468 – 3D item model glitch
- MC-79612 – NBT accounting incorrectly allows for giant allocations of empty lists
- Private issues