Crash when entering or exiting a world, or starting the game, while on a resource pack

After switching to the resource pack Simplify, launching the game, entering or exiting a world results in a crash.

What I expected to happen was...:

• In case a: The world loads.
• In cases b and c: The main menu loads.

What actually happened was...:
In all three cases: the game crashes with a crash report like that in the attached text file.
Update: The case a crash no longer occurs in Minecraft 1.6.2.

As a workaround to case c, move or remove Simplify before launching the game. Minecraft will revert to the default pack.

Steps to Reproduce:

1. Download Simplify and place it into the .minecraft/resourcepacks folder.
   • Note that the zipped version does not appear in the resource packs list.
2. Unzip Simplify into the .minecraft/resourcepacks folder.
   • Note that it shows up now.
3. Switch to Simplify.
   • Everything works fine when using another resource pack, such as oCd.
   • Note that the game does not crash yet: this is not the same as MC-17831.
4. There are at least three ways to reproduce this:
   • Case a: Try to enter a singleplayer world or multiplayer server.
   • Case b: Try to exit the current world (press "Escape", click "Save and Quit to Title" or "Disconnect").
   • Case c: Quit Minecraft and launch it again (click the "Play" button in the MinecraftDev launcher). In this case, the crash occurs after the Mojang logo is displayed.