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."