[1.8] Custom Item textures do not unload properly between worlds

Partner Rank: 

2

Partner Team Reporting:

Polymaps

Verification builds:

ver. 1.8.0.4, build 1235442, Win10

Summary:

Item textures displayed in the hand will not display the correct texture if a map was played before (in the same session) which uses custom textures.

Impact:

If a player is playing multiple maps in the same session, then textures from one world can end up on items in another world. This can impact gameplay when textures aren't what the player is supposed to be seeing. e,g, candy cane swords in a space world.

Repro Steps:

1. Create a new world using the "Santa's Sleigh Ride" world template.
2. Once the world has opened, Save and Quit to the main menu.
3. Create a new world (randomly generated) in Creative mode
4. Give yourself: Diamond Hoe, Iron Hoe, Golden Hoe, Stone Hoe, Wooden Hoe, Wooden Sword, Bread, Snowball.
5. Notice how the textures from Santa's Sleigh Ride are appearing in your vanilla world.

Observed Results:

Textures from Santa's Sleigh Ride appear in the vanilla world. See video for an example!

Expected Results:

Items should load the correct texture per world.

Screenshots/Videos attached: Yes/No

https://www.youtube.com/watch?v=fhzvB5hkoZI

Regression Builds:

vers. 1.7.9.0

Notes:

The video shows the bug in action