In my main world (made in 0.5) (creative), I used the Make Infinite button and went to my animal spawners and saw that they had lost the cage around them and they were unbreakable. The issue did not affect all spawners, but it did most of them. Now that I have built something else there, there are cows and sheep everywhere! (Note: The spawners act like they are not there because water can flow through them.)