After hearing that the B snapshot added the ability for carpet to be placed on iron bars, I went to test it. I started trying various things and realized that the limitation on what carpet could be placed on was removed. This might not be good in some situations, though. At the very least, they don't make sense.
The screenshot attached shows several examples. From left to right without listing intended examples, carpet on: Ladder, Water Source Block, Lilypad, Steve Head, Upward Facing Piston (Can also be on Sideways Facing Piston without breaking and the Extended Piston Head), Torch, Chest, Flower, Unpowered Rail, stacked on top of each other, End Portal Frame (Which also relates to an older problem listed elsewhere on the site), Beacon (Can still work through carpet, which while useful is odd), Button, Cactus, Bottom Half Slab, and Sapling.
While it could be useful in some cases, the ability should probably stay within reason. It should at least be sitting on some surface directly. Examples like the Steve Head, Torch, Flower, and Button probably shouldn't be possible.