Another Anvi bug

What i expected to happen was for the anvil to fall with normal anamation.

What happened is when i placed anvil and let it fall, when it fell the anvil did a 90 degree turn while falling and turned back when it landed.

1. make a stone tower (1 by 1 by any hight)
2. place anvil at top of wall on a side.
3. observe from top of tower, if there is no bug apparent, chose a different side to place it on. look at all sides.
4. observe.