Pistons no longer reliably push entities, mobs, and also "disappear"

Demonstration can be seen here http://www.youtube.com/watch?v=-HhVJ4Xbjd0 (after upload is complete - approx. 17 minutes from the time of post)
Pistons unreliably push entities and mobs alike. The pistons also visually disappear when retracted too fast.
I forgot to showcase in the clip, however they are not "ghost" entities, as they can be picked up after removing the wooden retaining block.
Happens in Creative, survival, and Adventure.
Showcased in a single player, offline (No LAN) game. Untested in Multiplayer