After the last snapshot I started creating a texture pack, and adding some subtle animations to some of the blocks. For each of them, I created the associated [block].txt file. After upgrading to 13w09, the blockRedstone no longer functions, and is replaced by the "missing texture" block.
Other custom animations (i.e. the nether portal) still function. Perhaps the issue is with blocks that aren't originally animated? Both the png and definition file that were previously working are attached.
Replacing the texture with a single 32x32 png and removing the animation definition allowed the texture to appear in-game again.
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Duplicate of MC-10355, please use the search function to see if your bug has already been submitted. Currently over 52% of tickets are being closed as duplicate.

@Tails & @Thorogood:
Would you at least upvote MC-10355 and add any sign of confirmation apart from "Dublicate of ..." ?
I still don't know for sure if it's only on my side or happening for many others too, but Thorogood seems to have the same problem.
Apologies. I searched for "animated", as opposed to just "texture pack" since only animated files were being affected, and the results did not come up with anything whatsoever, only showing results for "animals" instead.