When a chicken jockey spawns in the world, after killing the zombie riding it, the chicken will not lay eggs.
For a while I thought this was a feature, but I have recently been told it is a glitch. I assume this glitch is present in past versions as well
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There is MC-42174, however it does not mention what the intended fix is. Chicken jockeys can despawn, so maybe that was the fix and it was an oversight that a chicken whose rider was killed does not become a regular chicken.