Multiple mobs spawn on one block at the same time

Steps to reproduce

1. Watch mobs spawn naturally.

Expected result

Each mob spawns on its own block.

Actual result

Sometimes mobs spawn 2-4 all on one block, then split apart from each other.

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Original description
I don't know if this is a bug or not, but mobs spawn on the same one block. It looks like multiple mobs going out from one. I see this very often and it's a weird sight.