@Tails
The problem seems to be fixed in MC1.7.2/Launcher 1.3.3.
That is likely Block 36. Right-click it, and if it disappears, then it’s Block 36 and not a bug.
That's odd, for me only named horses don't move.
Edit: I punched it, and it started moving again.
Are there any spawners around you? Right now they are crashing in 13w21a
Yeah same happened to me. I was working on my CTM Map (spawners of course) and it kept crashing. I didn't know it was from the spawners though.
Crash report attached.
@[Mod]Ezekiel
Due to recent updates, I cannot spawn the piston head anymore to test this. I do not think this is a concern anymore.