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Added crashreport while streaming.
Seems I can't edit the affected version, though I'd like to add that it also happens in the 13w02a snapshot.
This happens a lot more (50% of all new worlds I start) with the 1.4 series where I didn't have them before (<1.4). My OS = OX X 10.8.2. Java: 1.6.0_37
Cow, pigs, and sheep can't seem to jump over 1 block 1 obstacles. Chickens however can.
Confirmed on OS X Mavericks, Java 6 update 65 on the 14w31a snapshot.