Confirmed for 1.6 pre. It's even worse with horses. They walk into blocks and suffocate very often, even without reloading any chunks.
This is really annoying. In a new survival world, I wasn't able to get a proper cow farm going (starting with 2 cows) because every single time, the baby cow escaped or ended up suffocating in 2 thick cobblestone walls.
I really hope you can address all this buggy mob behaviour soon.
Maybe if they changed the sound? A splashing noise would make more sense to me than a block breaking sound.