All three of the ones in the other dimensions are ghosts
Also happens in the Nether (in both the worlds)
Also happens in the End, although this is probably trivial if you're trying to shoot a dragon that's a hundred metres away and automatically regenerates its health.
Obviously the one without the cobblestone is the second one because you can't actually put them there without them attached to a block.
Confirmed; they are ghosts
Nope; it's only if the "Re-Create World" function is used. I did not go into any other dimensions.
This issue doesn't seem to happen in 1.7.4 anymore. Could someone please confirm?