The file stitched_items.png (which seems to end up in different places on different machines) has some textures doing strange things, such as overlaying each other, e.g. comparator, hopper, nether brick, and nether quartz (all new items?) are all overlayed on the nether quartz ore texture, and some items seem to have been shifted and overlayed on themselves.
This file and stitched_terrain may well be just for debugging, and may be removed soon, but I thought it best to file a bug report anyway.
... Huh. Thanks!