1.5.2 and 1.6.1 spawn different animals in the same location being provided the same particular seed

The same world (same seed == 12345) is populated significantly different if being created in 1.5.2 and 1.6.1.

First two screenshots show two particular places of the world created in 1.5.2 using seed 12345. These places are populated by numerous pigs and chickens respectively.

Next two screenshots show the same world (seed 12345) created in 1.6.1. It turned pigs and chickens into horses and sheep. So chickens became extremely rare on this location now.

I tried few seeds. Some do have this issue, some other do not.