Well, dang. Let me see if coloring the whole thing white will work to disable shading... EDIT: Nope. Birch leaves don't even seem to change color when the colormap changes. Jungle leaves respond, but nothing else does. EDIT 2: Yep, birch leaves do not obey foliage.png - replacing the game's own files does not change the birch leaves. I wonder what's shading them, then...
That would certainly explain it, but just one more note - none of the leaves texture in the resource pack are greyscale. Anyway, let me try some stuff and thanks for all your help!
Hmm, yeah, you're right. The only problem is my foliage file is completely blank - all pixels are #000000 and completely transparent. I guess MC is using the default foliage shader in its place, then? I can try again with another biome shader and see if that changes anything.
@Th3: The foliage file is entirely transparent, but the problem also occurs with the default foliage shading.
@Tails: The bug seems to be resolved as of 1.4.5 - pressure plates and commandBlocks work very nicely now.
That seems completely correct. I'll go ahead and open a more specific bug report on this issue. Thank you so much for your help!