This bug has been present since the introduction of anvils.
Place an anvil and fly to it's sides. Your player will be glitching a bit. Also, this can happen while falling, hitting it's sides. Player will glitch like there wasn't a block in client, but there was in server side. Might take a while to do this though.
- duplicates
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MC-1669 Possible to walk through two perpendicular anvils at the corner where they meet.
- Resolved