To recreate the bug u must put an falling block(like sand or even an anvil) and on top of it an anvil. If they fall for more then 2 blocks and end up on something that will make them pop(like carpet) only the anvil will pop and the other entity will disappear .
Here's a video of me recreating it: https://youtu.be/4salGay0Z3M
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We're tracking this issue in MC-572, so this ticket is being resolved and linked as a duplicate.
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