Chickens escape fence in 14w08a while they do not in 1.7.5.

Captured video attached for both versions.

The chickens appear to simply get pushed right through a fence that would normally contain them - baby and adult chickens alike.

Capture.zip contains:
javaw_2014_02_27_21_53_36_536.avi - version 1.7.5 - chickens contained
javaw_2014_02_27_21_57_01_176.avi - version 14w08a - chickens uncontained