Not sure if this is really a bug and I don't think it's that big a deal since it seems like it can only happen by putting multiple rabbits in a one-block area they can't escape from, but I thought I should mention it anyways since it's kind of interesting.

If you spawn a bunch of rabbits like in the screenshots, then jump down to split them up, they generally split into two groups, and if you spawn more rabbits right in the middle they will kind of just shift right into one of the corners where the groups are.