Animations for items and blocks do not work properly

All animated items and blocks (except for water, lava, fire, portal, clock and compass) are rendered white with the text "missing texture" on them instead loading the respective animation texture. I made sure all animations have their own txt-file (as required in Snapshot 13w09a).
Everything worked fine in the previous snapshots and there is no way to get them running, even with a proper txt-file for every animation, so this seems to be a massive bug.

Screenshots and test files attached below ...

How to use the test files (showing an animated Monster Spawner):
Move "mobSpawner.png" and "mobSpawner.txt" to the "/textures/blocks"-folder in any converted texturepack, start the game and test your Monster Spawners.

EDIT:
Added a small test-texturepack to the attachments containing the shown monster spawner animation
EDIT 2:
When testing it with a folder-based texturepack, it seems to work fine, but the game doesn't load the animations from a zip-folder.
EDIT 3:
Further testing of folder based packs showed that compass, clock, flowing water, (+flowing lava?), portal and fire animations are broken, but all other animations work fine.

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Comment from Kahr:
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"I suspect the problem lies in bji.class. The method "public boolean c(String)" which checks if the texture pack contains a given file does not strip off the leading slash from the path. Adding a .substring(1) before calling ZipFile.getEntry should fix it."